This was originally intended as a longer comment, but the previous draft unfortunately blinked out of existence… Though, I’m more than willing to shed some light on the distros discussed below if you’re interested.

Or any other Good KDE Distros out there.

I’m surprised that no one else has mentioned them yet. Thus, for the sake of completeness, consider Aurora and Bazzite. It’s what I would personally install/recommend for/to relatives/friends that would like to make the switch to Linux.

Pop!_OS’ Cosmic DE is a recent fork of Gnome. It’s the fourth “No, I’d rather put up with being a FOSS project manager for the rest of my life than keep using Gnome” DE I’m aware of, after:

• MATE is basically “No, we like how Gnome 2 was, so we’re keeping it.”
• Cinnamon is basically "GTK3 is cool but we’re not doing all this “almost nothing works because you HAVE to use it EXACTLY like this” crap. Linux Mint is basically a grievance distro; it’s defuckulated Ubuntu with defuckulated Gnome.
• Unity. Because Canonical was reinventing the wheel, the inclined plane, the lever, human speech, electromagnetism, fire, antiperspirant, package management, the display service and the init system, so why not the DE as well?
• Cosmic. I’m not sure why System76 bothered, other than Gnome wasn’t sparkly enough.

Onto your actual questions:

1. I don’t know if Manjaro is European or not, but I have given up on them. They’ve made a lot of rookie mistakes like letting security certificates expire, they dropped the ball pretty hard with the PinePhone IIRC, and every time I’ve attempted to use Manjaro it just didn’t work that well.

Pop!_OS is the in-house distro of System76, a for-profit computer vendor based in Colorado. It’s meant to work well on their hardware out of the box; the big claim to fame that I saw when they were the trendy distro of the week is they had a version that had Nvidia drivers baked into the install, so to the end user “If you have an Nvidia card, click the link on the website that says Nvidia and it works.”

Linux Mint, as previously mentioned, is mostly concerned with distancing itself from questionable decisions made by Ubuntu and Gnome. It maintains compatibility with Ubuntu, so Ubuntu install instructions for software pretty much always work with Mint, and yet the DE is more easily understood by Windows users.

Fedora is Decommercialized Red Hat, honestly I don’t really see them making much effort towards beginners besides maybe their immutable/atomic versions.

Customization of KDE is going to be pretty similar if you stick to things you can change via the settings menu, at some point during “customization” you’ll find the boundary between DE and distro. Yes, many people use KDE. Unlike Gnome, they haven’t pissed off four different groups over the ages resulting in forks. KDE is mighty popular.

“Is it really beginner friendly, snappy, stable?” Lots of things “it” could be, if you mean KDE…yeah? I personally prefer Cinnamon as a “give to grandma” OS because KDE tends to slop more crap on the screen, especially in that One Settings Menu To Rule Them All they have. This is a subjective experience but, if I ever found myself thinking “Is there a setting to change this?” I felt more able to find that setting in Cinnamon than in KDE.

2. I know very little about OpenSuSe, I’ve never once tried a SuSe-based distro.

3. Out of the three you listed, I’d go with Fedora. I’m typing this on a machine running Fedora KDE. I would personally recommend KDE Neon or Kubuntu before Manjaro or OpenSuSe. Manjaro because I’ve had bad luck with Manjaro, and I have no experience with SuSe. I might also steer you to EndeavourOS or vanilla Arch over Manjaro.

You’ve used the word “stable” a lot. Users typically mean “is it going to crash?” None of these are going to crash, you’re not going to crash Linux. What you might find, depending on the distro, is someone will push an update to a software package that breaks your workflow. Debian Stable, Ubuntu LTS, distros like those do point-in-time feature freezes to avoid that possibility. You might not get the newest features but your system will continue to work like it always has. Rolling release distros like Arch push updates as soon as their developers release them, so you get all the cutting edge features, bugs and breakages.

Of the three you listed, Manjaro will be the least “stable” by that definition; it’s a fork of Arch. Fedora and OpenSuSe are both forks of commercial distros so you get that less, but I can attest on Fedora it does happen, they broke the lock screen last month. You want to never reboot your computer to find something suddenly doesn’t work, go with Debian Stable.

I started with Opensuse Tumbleweed about 2 years ago from almost 0 knowledge and never looked back.

Lot’s of great answers already. I’ll just had my thoughts and hope it helps.
Choosing a Linux distro is fucking hard, but the good thing is that you already have a DE (Desktop Environment) that you like, KDE Plasma (KDE is the community, Plasma is the name of the DE) and it’s my favorite.

1 - Manjaro was my first distro for daily use. I would not recommend it, i don’t think it’s stable enough to get into linux. Would not recommend any Arch based distro.
2 - OpenSuse is an old distribution, but not beginner friendly, so maybe not a good idea to dip your toes into it.
3 - Fedora is well established with lots of documentation, a big community and a 6 month update release model that should give you the newest features very fast while still maintaining stability. I don’t recommend the Atomic distros. If you’ve already installed and it works then stick with it for a while.

There are also the Ubuntu based distros like Kubuntu, KDE Neon or Tuxedo OS. Ubuntu has probably the largest user base, so documentation is abound everywhere regardless of the distro you pick.

You’re already testing out different distros, try to daily drive for a month and read up on what makes them different. In general it’s how to install software, the release model (“Long Term Support” or “Rolling Release”) and the core system. Apps are installed on top of the system and right now come in a variety of formats. I strongly recommend that you enable Flatpak on the distro you chose and use the Discovery app for software management.

Edit: Added “Tuxedo OS”

I’ll give a contrasting opinion.

I’ve used both Fedora and Manjaro extensively, and I prefer Manjaro.

The reason is that I prefer the package management of Arch more than fedora. I’ve had no issues finding what I need through the official arch repositories and the AUR (secondary choice).

Manjaro is a bleeding edge distro so keep that in mind. Personally, I’ve had no problems in the last year of running it.

Linux Mint is actually fast, and uses half the RAM of Fedora (see shots: https://files.mastodon.social/media_attachments/files/114/653/604/229/121/661/original/6d60399683784c13.png and https://files.mastodon.social/media_attachments/files/114/761/028/826/681/916/original/32f1c276089be277.png ). With a bit of tweaking, and using the Cinnamenu menu instead of the default one, it feels really good. On Fedora KDE I got updates every couple of days to the excess of 1 GB. I’m on 50mbps internet, and that was too much for me.

OpenSUSE Tumbleweed is pretty solid and 98% of the refinement of Fedora, that in my opinion, it is the most polished of them all. Now, using Fedora supports companies like Red Hat/IBM so it is a no-no for me.

The only thing OpenSUSE has is that is independent so does a few things differently than Debian or Fedora based ones, but after a few retouches that you will learn in no time you will be at the level of Fedora. It is perfectly OK for beginners, just that there are a few things differently, sometimes for the better like many utilities from YAST, but will be different from what you find in most non OpenSUSE forums. Again, is minimal, 95% of the staff is the same. Unfortunately, it does not have the costumer base that Ubuntus/Mint/Fedora has, but the supporters are technically highly committed and competent, they just need to improve in their marketing arena that is what is holding them down.

Another KDE that I like is TuxedoOS. It works perfectly in non Tuxedo devices and very stable in my experience… I even had better stability experience than Kubuntu, and that says a lot.

Did not play enough with Manjaro and will try in a few days. It had some bad press but I think is more due to diverging a bit from Arch philosophy of instant updates than anything else. CachyOS I recommend only for latest computers or those willing to adjust things a bit once in a while.

For older devices, MXLinux KDE is the ideal in integrated graphics chips.

openSUSE and Fedora with Plasma will be fine choices for you, based on this. Tumbleweed will take a bit more work, but usually it’s nothing too difficult. You can also go with Leap, which generally won’t have the same issues Tumbleweed has. I personally use Tumbleweed and like it a lot.

Fedora is just an all around solid distro, endorsed by Linus Torvalds himself! In my opinion, since you already have some experience with it, stick with Fedora. It’ll be fine.

CachyOS!

https://cachyos.org/

It’s like Manjaro but better, and highly KDE focused. TBH… don’t use Manjaro, SUSE is much better than that.

Use Fedora workstation or Fedora Kinoite if you want an atomic version. If you just want a system to work and you don’t care to tinker much I highly recommend Kinoite as it won’t break easily on you and is very stable.

If you install the latest Kubuntu with backports enabled, you can get a newer version of KDE than the one that comes “stock” with Kubuntu. The KDE version isn’t as new as KDE Neons’, but still newish.

openSUSE Tumbleweed is the rolling release, where you may have dependency decisions to make during regular updates. Updates must be done in the terminal.

The more beginner friendly version is openSUSE Leap. That has a longer release cycle, and you use the Discover interface (or yeast, or zypper in the terminal) to update.

Either is pretty friendly. Both have recent KDE.

Fedora KDE pretty much offers the best KDE Plasma experience, maybe right after OpenSuse.

If you are still using Fedora, I recommend sticking with it. It doesn’t get much better than that.

there’s:

• KDE neon (sorta dodgy but always has the newest KDE release on top of ubuntu)
• Kubuntu (KDE on ubuntu but a bit old)
• Debian+KDE (KDE but a good few months old)

I wouldn’t recommend manjaro, they’re very dodgy

Opensuse is pretty good, iirc they have a GUI for most configuration items and you get the newest packages for everything. it’s like easier arch