Alpine Linux.

Regarding your post formatting, you need to put a space between the bullet point and the first character of the line:

• Like this (hit view source/view markdown on my comment to see)

kde neon don't use snaps

Debian stable.

@Luffy879 If someone comes from Windows and has little experience with Linux Mint LTS with XFCE4.
https://www.linuxmint.com/edition.php?id=313
With MX Linux (Debian based) you can create a live ISO with all packages and flat packs and then create a live USB stick with persistence (requires double memory on the Linux partition For the ISO)
https://mxlinux.org/
you can make installs from the usb after creating it.
Distrochooser
https://distrochooser.de/

Sorry, the closest i came up aren't good solution but may help in your search.

• Vanilla OS 2 (based on Debian) but it is under Gnome DE and in beta phase. Very begginer friendly. Maybe once it go out from beta it will supports other DE ? So check it around 6th month later or 1 year ?

But the problem is that their community is very small. If you want something stable, it's better to look for bigger community so you can benefit from their support and user's problems

There is fedora kinoite but you don't want anything related to IBM. That was the best compromise i can found.

• NixOS but i don't know it. I'm affraid it will be a DIY distro at the beggining with the config file. But it will probably meet all your criterias.

Or the same OS from my steamdeck :

• Steam OS ? It's an immutable OS based on Arch and support KDE by default. Full support of flatpaks. Only downside, i dunno if it supports other machines than the steamdeck. Nor if it uses the latest linux kernel. Maybe some variants ?

What about Pop!_OS? It fits all the criteria. It's an Ubuntu distro by System76 (known for their computers that run Linux) that foregoes Snaps for Flatpaks, so you get Ubuntu's reliability/stability without the Snaps. It does default to its own spin on GNOME, however you can install an alternative desktop environment just fine.

yes Debian, install latest MX Linux (23.2 AHS) and enjoy it, it's a great distro, up to date, well maintained. There is a KDE version where you can install latest kernel from their AHS repo (6.6.11 as time of writing)

disable repositories, updates https://github.com/aarnt/octopi, https://ctlos.github.io/, https://endeavouros.com/.

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.

Debian Stable as base OS, then activate unstable repos in a sandbox/container. Maybe even Distrobox for newer Apps.