see latest notes there (you need llvm 15.0.4 -  yeah, in this case 0.0.1 version matters) and mesa git + some merge requests manually merged, but results relatively promising - darktable starts and enjoy some 2x speedup (on Power CPU, no less!), Lux render also starts and works.

Ffmpeg I guess not tested yet :)

for me ffmpeg -filters | grep opencl shows

... avgblur_opencl    V->V       Apply average blur filter      ... boxblur_opencl    V->V       Apply boxblur filter to input video    

... colorkey_opencl   V->V       Turns a certain color into transparency. Operates on RGB colors.                            ... convolution_opencl V->V       Apply convolution mask to input video

 ... deshake_opencl    V->V       Feature-point based video stabilization filter                                                        ... dilation_opencl   V->V       Apply dilation effect          ... erosion_opencl    V->V       Apply erosion effect            ... nlmeans_opencl    V->V       Non-local means denoiser through OpenCL                                                    ... overlay_opencl    VV->V      Overlay one video on top of another    

... pad_opencl        V->V       Pad the input video.             ... prewitt_opencl    V->V       Apply prewitt operator         ... program_opencl    |->V       Filter video using an OpenCL program  

 ... roberts_opencl    V->V       Apply roberts operator       ... sobel_opencl      V->V       Apply sobel operator          ... tonemap_opencl    V->V       Perform HDR to SDR conversion with tonemapping.

  ... transpose_opencl  V->V       Transpose input video   

 ... unsharp_opencl    V->V       Apply unsharp mask to input video      

... xfade_opencl      VV->V      Cross fade one video with another video.                                                                       ... openclsrc         |->V       Generate video using an OpenCL program

for tonemapping on OpenCL this line was suggested (on Nvidia) - see below.

so I guess we can use it as example for trying on Radeons (comment about OpenCL 1.2 needed still apply, but rusticl exposes 3.0 :-) )

there is also AUR package, but not sure if it tracks right branch from Karol Herbst (developer) repo ..

I personally look at 

note enabling this also require some environment flags to be set.

ffmpeg -vsync 0 -hwaccel cuda \

 -init_hw_device opencl=ocl \

-filter_hw_device ocl -extra_hw_frames 3 \

-threads 16 -c:v hevc_cuvid \

-resize 1920x1080 -i INPUT \

-vf "format=p010,hwupload,tonemap_opencl=tonemap=mobius:param=0.01:desat=0:r=tv:p=bt709:t=bt709:m=bt709:format=nv12,hwdownload,format=nv12" \

 -c:a copy -c:s copy \

-c:v libx264 -max_muxing_queue_size 9999 OUTPUT