SOLVED: Playback error "This client isn't compatible..."

[Representing_all_cats]

Soooooooooo... I finally got home to test the client again, but while I was away, I found this open issue: https://github.com/jellyfin/jellyfin/issues/8292

It turns out that this was the exact same problem I was having. Both files I tested previously played using the workaround in the link. Hope this can get a proper resolution in a future update!

Thanks for the help @TheDreadPirate and @Venson!