In my experience, transcoding with subtitles becomes an issue when the subtitles are burned in to the video. I often get external subtitles from https://www.opensubtitles.org/ and then stick the downloaded SRT file in the same folder as the movie. Make sure it has the exact same file name as the movie so jellyfin will associate the two together. Once I do that, it does not transcode at least for subtitle reasons.

Let’s not get carried away now

Still better than Jennifer Null I guess