Linux

Opensuse Slowroll

Alpine Linux.

OpenSUSE TW

it should be more or less stable, comparable to Ubuntu with or without LTS

It’s very stable and I’ve never had issues

it should not be related to IBM to any way (so no fedora/redhat)

It’s supported

no DIY Distros

It’s developed by SUSE.

it should not feature snaps (no Ubuntu or KDE neon)

It uses flatpaks

KDE plasma should be installable manually (best case even installed by default)

OpenSUSE is one of the few distributions that uses KDE Plasma by default.

Just to clarity the relationship between Red Hat, IBM, and Fedora, Fedora is only sponsored by Red Hat. They make all their own decisions, and while they receive financial support from Red Hat and Red Hat owns the Fedora trademark, their decisions and development are independent of Red Hat (and by extension IBM), with the single exception that they cannot risk violating the law (i.e. copyright infringement), else it risks Red Hat legal trouble (and Fedora would risk losing their sponsorship as a result). Red Hat benefits from Fedora's development by the community, given that Fedora is RHEL's upstream, hence why it continues to sponsor Fedora. But it isn't Red Hat that is in charge of Fedora's development, it's FESCo, which is entirely community elected, and does not stand for the interests of Red Hat, but rather for the interests of the community.

Eliminating Fedora from contention in that regard is essentially like eliminating Debian because you don't like Canonical, who makes Ubuntu, a downstream of Debian.

Add on top of that the fact that IBM and Red Hat are major contributors to the Linux kernel, and you absolutely cannot avoid connections to them while using Linux. I mean, that's quite frankly a ridiculous exclusion criteria in the context of Linux. If you're looking to avoid an operating system OWNED by Red Hat or IBM, then Fedora should not be included in that list. Neither of them have any say or pull in the development of Fedora, which is a completely community-driven project (no, owning the trademark doesn't change that fact; if Red Hat tried to take over, the Fedora community would simply fork the project, rebrand, and continue on their own). Besides, Red Hat has no interest in controlling Fedora, because it doesn't benefit them. Their only interest is in enterprise applications, which is not a good use case for Fedora. The only operating systems Red Hat actually has any control over are RHEL, CentOS, and any derivatives of those operating systems like Rocky Linux, Oracle Linux, and such (though Red Hat's control over derivatives was only the result of those projects being downstream, not actual ownership).

So with that in mind, I'd recommend the Fedora KDE spin if you want a normal, stable, snap-free, no DIY required distro with KDE, or if you want the immutable version, Fedora Kinoite is what you'd be looking for. And Fedora has the major advantage over Debian-based distros of actually receiving package and kernel updates regularly, so you can stay up to date and enjoy new features, all while maintaining stability.

Fedora Kinoite is absolutely the best immutable distro fitting your criteria. Anything else will have a much smaller community and less support as a result. rpm-ostree has great documentation, and all of the Fedora Atomic Spins have a huge userbase available in case you ever have questions.

debian (mx-linux has a kde version if you want less hasle then pure debian) or opensuse leap on the "stable" side, opensuse tumbleweed if you want more recent packages (i've never had it destroy itself like arch, its been very stable for a rolling distro)

I would recommend void, alpine (kde plasma auto installer may still be broken for some users, works for me tho, also musl so if you need appimages or some very specific applications don't use it.), alpaquita (much stable alpine with glibc if you need appimages), slackware (current only, it is stable rolling, and their point release features very old kernel and packages so I wouldn't recommend it, paldo (stable rolling, gnome by default but plasma installable.), gentoo (if you have time to compile, why not it as stable as rolling can get without it being openSUSE), openSUSE (easiest rpm based (Oracle fork) but still IBM code nonetheless)

Gentoo.

It's rolling release, has stable and testing packages, and users can choose between them per-package (or globally) and it runs or is easily made to run on pretty much everything.

Slackware current.

OpenSUSE. snapshots build in. nVidia hosts its own Leap or Tumbleweed GPU repo you can add for trouble fee GPU use. GUI for almoat all config tasks you might normally do at the CLI. Stable...and rollbacks ahould you make a mistake

You can't avoid IBM/RedHat - they contribute to the kernel and many, many other parts of Linux eg systemd. I have no idea what you mean by DIY distros, what a peculiar adjective in this context. Linux itself is DIY. Life is DIY.

That said, voidlinux is an independent distro without systemd or snaps based on runit for init and xbps for package management. It's also a STABLE rolling release.

There are only 3 options I can immediately think of, for you:

Debian

OpenSUSE (Leap)

Slackware

They are ordered from most to least likely to recommend for your criteria i.e I recommend Debian, alternatively Leap, and if you don't like either you can try Slackware, but Slackware is closer to a DIY distro.

I read this as:
Looking for a Half-Life Linux distro

Omg you just described slackware. Join us!

I would recommend Fedora Kinoite.
Yes, you said no RedHat stuff, but Fedora is 100% community run.

Especially when you use the Kinoite-build from universal-blue.org, everything should work ootb and is very reliable, while also being semi-stable in terms of update frequency

An immutable distro with a heavily customized KDE desktop is Nitrux. Check it out at nxos.org

Debian as others are saying is a great choice

But I'll still shill arch, I've literally never encountered a problem with it other than my first time installing manually being a learning experience. Not sure if it counts as a DIY distro bc you can definitely install with a script

• Siduction
• openSUSE

OpenSuse seems like it would meet your needs. OpenSuse Kalpa might be one to look into since it's immutable and features KDE Plasma

Linux Mint is hands down the most stable linux distro out there and has been for years. zero tinkering needed. everything just runs no questions asked.

My only grief with Mint is the most recent update where they changed the software centee and now it's slowed to a crawl. Why they would do this is anyones guess.

I'm recommending MX until such time that Mint sort their crap out - unfortunately I doubt they will, seeing as this change of software center was to resolve some other issues they (but not is end users) though they had.

MX is basically debian but with a lot of improvements. Sure it might have a bit of a learning curve for those primarily used to Ubuntu based systems, but it beats running any of the other Ubuntu distros by miles since they all struggle with the crap Ubuntu puts on top of Debian.

Manjaro is another great option if you don't want to deal with debian based stuff, and KDE is the default DE with most stuff under reasonable control. You can also use all the Arch resources if you ever run into trouble so it's a lot less of a headache than what I've experienced running OpenSUSE (i want to love OpenSUSE but I just can't).

Debian? Just make sure you use backports, containers or flatpak if you want newer software.

Same recommendation as usual from me :) pepparmint OS , Debian base extra on top

If Debian is too DIY for you, then you could try LMDE with the BTRFS filesystem and Timeshift for maximum safety and far less DIY.

• yet another vote for Debian
• or if you’re going immutable (“atomic” is a better name) then wait for Vanilla OS’s Orchid to be released (currently in Beta) – a little more user-friendly than NixOS (although that will depend on the documentation)

I never understood the IBM/Redhat hate being directed at Fedora. Imagine being against using Debian because of the Ubuntu Amazon fiasco that happened years back.

Seems that Slackware is what you are looking for.