How to know if the HW acceleration is working

[SKAL]

As far as I know, you need to both pass in the /dev/dri/renderD12* device into the container and ensure the user running Jellyfin (UID 1000 in your case) has access to the render/video group on the host. Group name differs by distro but I don't think passing in the card as you have will work. Either send the entire /dev/dri directory or go with the render device.

one step forward one step back...
in order to avoid any problem, I've decided to remove the user: 1000:1000 in the compose file.
now in the docker jellyfin works as root so it should be able to access to all the files.

now I have a new problem

If I run inside the docker

# lspci -k
[...]
00:02.0 VGA compatible controller: Device 1234:1111 (rev 02)
        Subsystem: Red Hat, Inc. Device 1100
        Kernel driver in use: bochs-drm
[...]
00:10.0 VGA compatible controller: Intel Corporation Device 46d2
        Subsystem: Intel Corporation Device 7270
        Kernel driver in use: i915

I can see both the devices,
but if I try to run the
# intel_gpu_top
Failed to detect engines! (No such file or directory)
(Kernel 4.16 or newer is required for i915 PMU support.)

as you can see I get this error. This means that the i915 is not accesible?
but the module is loaded

# lsmod|grep i915
i915                3055616  0
drm_buddy              20480  1 i915
video                  65536  1 i915
drm_display_helper    184320  1 i915
cec                    61440  2 drm_display_helper,i915
i2c_algo_bit          16384  1 i915
drm_kms_helper        204800  6 bochs,drm_vram_helper,drm_display_helper,i915
ttm                    94208  3 drm_vram_helper,drm_ttm_helper,i915
drm                  614400  9 drm_kms_helper,bochs,drm_vram_helper,drm_display_helper,drm_buddy,drm_ttm_helper,i915,ttm



any ideas?