*qbittorrent

And one in the display

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I also found this, It’s for a RaspberryPi but surely can be adapted:

https://gist.github.com/seffs/2395ca640d6d8d8228a19a9995418211

You can look at the source of the snap and check what it does

I don’t have any experience with your exact question.

But I would look into xinit and try if you can start just mpv.

If this doesn’t work look for a slim WM and configer it that the applications are displayed in fullscreen and launch mpv after the WM.

Probably any of the tiling window managers should work: https://wiki.archlinux.org/title/Window_manager

+1 for nix, but I wouldn’t recommend it as a first distro

If you create an image of the disk in the current state from a live boot or an other machine. You can try fixing it without having to risk making things worse

I agree on your take, but I don’t think that “future scaling” is a concern for the most home users.