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

Ubuntu was based on Debian, which touts its stability

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

Debian has no afiliation to IBM, they're not even loosely part of each others' "partners" programs

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

Debian doesn't use snaps (welcome to the greener side of the fence btw, fuck snaps)

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

Debian uses KDE as one of it's default install options when installing the OS, and it can be installed later with tasksel (or by just getting all the packages if you want to do it the hard way)

-no DIY Distros

Debian has a barebones headless option, but the installer defaults (which come with the whole DE and oyher convenienve packages) are pretty user-friendly

In summary, I have no fucking clue what OS you should use.

P.S. newlines on lemmy are either done by using two spaces at the end of a line
and then pressing enter
(make sure your phone doesn't autocorrect/one of the spaces away like mine does) or by pressing

Enter twice (without the double spaces), so there's a

blank line in between