I used to run kodi on linux on intel NUC’s connected to all our TV’s a while ago. I don’t remember it being particularly unreliable. The issue that made me change that setup was hardware decoding support in 4k for newer codecs.
What I’ve had doing that frontend function ( kodi, jellyfin, disney plus, netflix etc ) for the last few years is three Nvidia shield TV pro’s which have been absolutely awesome. They are an old product now and I suspect Nvidia are too busy making money to work on a newer generation version of them,
The biggest surprise improvement was how good it was being able to ( easily ) configure their remotes to generate power on / off and volume up and down IR codes for the TV or the AV amp they were using so you only need a single remote.
Separating the function of the backend out from the frontend in the lounge has reduced the broken mess that happens around OS upgrades drastically.
Yeah, I reckon having a split of the frontend and the backend results in about half the complexity in each. If you have multiple frontends you can upgrade whatever the least important one is to see if there are any problems
I didn’t really answer your original question.
When I was using NUC’s I was using Linux mint which uses cinnamon by default as the window manager. Originally I changed it to use some really minimal window manager like twm, but then at some point it became practical to not use one at all and just run kodi directly on X.
If I was going back to a Linux frontend I’d probably evaluate libreELEC as it has alot of the sharp edges sorted out.