Rdlop's post in Hardware acceleration by using Docker was marked as the answer
cp /lib/firmware/arm/mali/arch10.8/mali_csffw.bin /lib/firmware
docker exec -it jellyfin /usr/lib/jellyfin-ffmpeg/ffmpeg -v debug -init_hw_device rkmpp=rk -init_hw_device opencl=ocl@rk
ffmpeg version 6.0.1-Jellyfin Copyright (c) 2000-2023 the FFmpeg developers
built with gcc 12 (Debian 12.2.0-14)
configuration: --prefix=/usr/lib/jellyfin-ffmpeg --target-os=linux --extra-version=Jellyfin --disable-doc --disable-ffplay --disable-ptx-compression --disable-static --disable-libxcb --disable-sdl2 --disable-xlib --enable-lto --enable-gpl --enable-version3 --enable-shared --enable-gmp --enable-gnutls --enable-chromaprint --enable-opencl --enable-libdrm --enable-libxml2 --enable-libass --enable-libfreetype --enable-libfribidi --enable-libfontconfig --enable-libbluray --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libopenmpt --enable-libdav1d --enable-libsvtav1 --enable-libwebp --enable-libvpx --enable-libx264 --enable-libx265 --enable-libzvbi --enable-libzimg --enable-libfdk-aac --arch=arm64 --cross-prefix=/usr/bin/aarch64-linux-gnu- --toolchain=hardened --enable-cross-compile --enable-rkmpp --enable-rkrga
libavutil 58. 2.100 / 58. 2.100
libavcodec 60. 3.100 / 60. 3.100
libavformat 60. 3.100 / 60. 3.100
libavdevice 60. 1.100 / 60. 1.100
libavfilter 9. 3.100 / 9. 3.100
libswscale 7. 1.100 / 7. 1.100
libswresample 4. 10.100 / 4. 10.100
libpostproc 57. 1.100 / 57. 1.100
Splitting the commandline.
Reading option '-v' ... matched as option 'v' (set logging level) with argument 'debug'.
Reading option '-init_hw_device' ... matched as option 'init_hw_device' (initialise hardware device) with argument 'rkmpp=rk'.
Reading option '-init_hw_device' ... matched as option 'init_hw_device' (initialise hardware device) with argument 'opencl=ocl@rk'.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option v (set logging level) with argument debug.
Applying option init_hw_device (initialise hardware device) with argument rkmpp=rk.
Applying option init_hw_device (initialise hardware device) with argument opencl=ocl@rk.
arm_release_ver: g13p0-01eac0, rk_so_ver: 10
[AVHWDeviceContext @ 0xaaaac71b4f00] 1 OpenCL platforms found.
[AVHWDeviceContext @ 0xaaaac71b4f00] 1 OpenCL devices found on platform "ARM Platform".
[AVHWDeviceContext @ 0xaaaac71b4f00] 0.0: ARM Platform / Mali-G610 r0p0
[AVHWDeviceContext @ 0xaaaac71b4f00] cl_arm_import_memory found as platform extension.
[AVHWDeviceContext @ 0xaaaac71b4f00] cl_khr_image2d_from_buffer found as platform extension.
[AVHWDeviceContext @ 0xaaaac71b4f00] DRM to OpenCL mapping on ARM function found (clImportMemoryARM).
Successfully parsed a group of options.
Hyper fast Audio and Video encoder
usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...
Use -h to get full help or, even better, run 'man ffmpeg'
dmesg|grep Mali
[ 367.986293] mali fb000000.gpu: Loading Mali firmware 0x1010000
[ 367.988606] mali fb000000.gpu: Mali firmware git_sha: 814b47b551159067b67a37c4e9adda458ad9d852
Seems the firmware not on the right folder see above :
