“If the picture is black but the audio is still playing, you should go back and select a stream with a different resolution.“
This is actually a fire stick specific issue relating to HDR 10 and Dolby Vision. TLDR is use the Kodi branch in this thread: https://github.com/jellyfin/jellyfin-androidtv/issues/2630 and inside that set either Dolby Vision or HDR 10, not both (the fire stick not being able to handle files with both is the bug.) Lastly, set the external player option in Stremio so Kodi is opened when you open a video
I would get a premium trial and share any playlists on the account you don’t want to lose for the development of your tool. Worked for me when exporting my 4000~ song playlist.