Any system can match those, once it’s configured and you keep it simple.

1. Any notifications can be disabled
2. Use a simple DE like Xfce, or a WM; also, turn off unnecessary services
3. Again, if you don’t install much, there’s less to cause conflicts
4. Should work with any distro

I like OpenSUSE Tumbleweed. Here’s how it aligns with what you’re looking for:

1. Notifications depends on the DE you choose; disable the automatic SW update checker and notifications will be minimal
2. Pretty much any DE/WM is supported, pick a low mem one
3. zypper dup every week or two and you’re good; make an alias if you’re lazy; if something breaks (very rare), boot into the old image and run snapper rollback and try updating again in a few days
4. I haven’t used OBS, but you probably need pakman repos for codecs; I doubt it’s more effort than opi codecs

Debian stable could also be a good pick, and it’s what I generally recommend. Just use FlatPak for most software and the older system packages shouldn’t be an issue. It may take more work to get OBS setup though, I haven’t tried.