@hlbkv
UT system is based on QT, whose graphic support on Linux is based on gstreamer libraries. Unfortunately by itself while wide, gstreamer support for advanced formats is not limitless.
You can find mkv sample files here
On Ubuntu 24.04 all files can be played by ffplay, even the invalid ones test4 and test7, while the standard gstreamer player (gst-play-1.0) can play 4 of them (2,3,5,7) if ffmpeg support (ffmpeg itself and the link library gstreamer1.0-libav) are not installed, and can play test1 and test6 if this support is enabled.
Ubuntu Touch can play 4 of these sample files (the same as desktop Ubuntu can play if ffmpeg support is not enabled)
gst-discoverer-1.0 test1.mkv
(...)
Properties:
Duration: 0:01:27.336000000
Seekable: yes
Live: no
container #0: Matroska
video #1: Microsoft MPEG-4 4.2
this 'Microsoft MPEG-4 4.2' is probably the same thing as your '10 bit support'.
You can install mpv with snap, it can probably play your mkv files.
Note that hardware support is not involved except when it comes to performance of course.