Subtitle burn-in won't use extracted embeded subtitles

[homelabResearcher]

jellyfin-ffmpeg comes with all the user space Intel media drivers except OpenCL, which is required for HDR tone mapping.  And the log you attached is indicates the video is HDR.  Because 22.04's repos don't contain a new enough OpenCL package for the N100, you will need to install it manually from Intel's git.

https://github.com/intel/compute-runtime/releases

Regarding it failing on Windows, there is a known issue with Intel's OpenCL drivers on Windows being broken.  You would need to revert to a November or December 2023 driver release.

Tone mapping is fine for other subtitles or no subtitle burn-in, I chose another subtitle and it worked perfectly fine as log shows. Also my Windows server is using NVENC. I believe reason why play starts slow is that ffmpeg have to probe through the whole file to find requested subtitle, which inherently can be solved by subtitle extracting. 
I will try to clean the extracted subtitles and try agian to see if the plugin ultimately fails to link these subtitles to original media, since for some subtiitles ffmpeg has to probe through the entire file, this process would be long. Hope you can give me some insights into how Jellyfin handles these extracted subtitles lol.