What advantages does it have over just 7zip?

This is indeed the correct answer. It is under the transcoding options. Your server will essentially need to re-transcode the video on the fly to add in subtitles. Which requires a not insignificant amount of processing power.

I ran into this issue while running jellyfin on a raspberry pi.

So long as your server has hardware acceleration turned on. To allow jellyfin to use your GPU for transcoding. You should be fine.

Ah yes, silly silly Larian studios. Why didn’t they think of this earlier!?

It’s so bloody hard to find one that’s below $100 and not a Zero model.

I’m pretty sure Lois is locking the door to prevent interruptions from anyone else.