Our Chromium is the same as Bullseye's, so don't install our test repo version. Debian removes the va-api feature for Buster, for unknown reasons. Our MystiQ just has a couple extra mkv presets that I found most useful, but you can get upstream Debian versions with my patch here:
https://build.opensuse.org/package/show ... ert/mystiq
We greatly prefer that MX packages be built in "clean rooms" using pbuilder or sbuild. This lets you build for any architecture that Debian supports on your machine, though in practice MX only needs Intel-type 32 and 64-bit builds. Plus your daily driver install can be as insane as can be--the packaging environments are in virtual boring vanilla Debian or MX setups (you can switch back and forth easily from Debian and MX by adding or removing the various MX repos to the build chroots)
Forget all you have ever been told about the "configure, make, sudo make install" way of building programs, which is way too much of a simplification. Backporting can make even complex packaging a breeze, though some can need a lot of tweaking.
There is a Deepin DE PPA that seems to have a manageable number of packages that may be good practice for the much larger chore of doing a newer KDE, and some users have asked for Deepin in our repos. I saw it at the Ubuntu Handbook blog.