This is a regular htpc build, not a mini PC, using this motherboard
https://www.asrock.com/mb/Intel/N100DC-ITX/
Since my last post, I ended up installing ubuntu 23.10 (which comes with kernel 6.5) and it's been very stable (always-on for almost 2 months, running a bunch of containers in addition to kodi). With 22.04 problems (freezes) started after a kernel update.
In kodi everything works except for playing AV1 content, trying to play an AV1 video causes an immediate crash, with or without AV1 VAAPI enabled. Maybe the ffmpeg bundled with Kodi 20.x is too old. I'm hopeful that kodi 21 + ubuntu 24.04LTS will fix this.
I use a BT USB dongle in this build to collect info from BLE sensors, it works very well, but this is different from the BT audio use case you mention below, for your use case I would use a BT "audio card" type dongle that is seen by linux as an audio card, zero compatibility problems, I used one many years ago. I don't use HDMI CEC so not sure about that.
Unfortunately the official team-kodi ppa is now unmaintained and no longer provides packages for recent versions of ubuntu. I ended up manually installing packages built for an older ubuntu release (working perfectly though)