Raspberry Pi 4 - 4k output?

Hello !
I’m fairly new to dietpi, been using it headlessly as a seedbox / plex media server with a 4TO USB Drive on a Raspberry Pi 3B+.
Recently updated to a Raspberry PI 4, using the same setup.
I’ve been wondering, since this new pi is 4K compatible, is it possible to install Kodi and also use it as a plex client?
I’ve tried this but the max resolution in diet-pi config is 1080p. Movies play fine on kodi + plex plug in, but in 1080p SDR (also can’t get HD Audio passthrough).
Is theory, is this setup doable? Is the rasp 4 not optimized yet? I saw the 4k output isn’t really stable even on LibreELEC.

Thank you for this great distro, has made my life a lot easier!