What is you choice for a media player?

[Hristo]

This one works best for me:

Install Clapper on Linux | Flathub

See also:

Librem 5 support VP9 on NXP i.MX8M

I selected from the Preferences in Clapper -> GStreamer -> Plugin Ranking -> vpx -> activated vp8dec and vp9dec. This was pure guessing, but helped. As I am still not sure what is the root, maybe someone has an idea on how is HW acceleration activated and how one can test that it is indeed used.