Haven’t read the whole thread, but am also having problems. For me the styling options are broken whenever audio needs to transcode only, as described in this thread: SRT subtitles cannot be formatted when audio is transcoded - #2 by Matt_K. Is it the same for folks here? (ie. if audio plays directly you can adjust the styling)
I also found that sometimes (rarely), when it’s not working, I can get some changes to work if I turn subtitles off/back on or otherwise force the player to redo the whole stream.