I would ideally like to convert the library to h.265 or even AV1 if I can make it work.
Unless you’ve downloaded remuxes (which I doubt), I’d seriously recommend redownloading instead of converting your existing files.
h.265 and especially AV1 take a long time to encode by CPU, and hardware encoding won’t give you any space savings, unless you’re okay with losing much details.
Redownloading is most definitely faster, will result in more space savings for the quality you’ll get. PS: Unless you’ve got data volume limits, but even then I’d recommend slowly upgrading over time. It’s quite simple with TRaSH guides and giving h.265 a higher score.
Client support is imo one of the major weak points of Jellyfin. Jellyfin itself does not need donations at the moment, but developers of various clients do [1].
But many client devs don’t take donations. E.g. Swiftfin links to Jellyfin’s OpenCollective page instead of taking donations themselves [2].
[1] https://opencollective.com/jellyfin/updates/were-good-seriously
[2] https://github.com/jellyfin/Swiftfin