If I’m not mistaken Jellyfin is actually a fork of Emby so they’re pretty similar, but one is a bit older.

Jellyfin forked from Emby in 2018 when Emby chose to switch to a closed-source model. Because of this, there are many similarities, but the projects continue to become increasingly different from one another as time goes on.

Basically a one-click install on supported devices. You just need a PC and a USB cable. Highly recommended

https://github.com/koreader/koreader/wiki/Installation-on-Kobo-devices

That alone does not prevent seeding. One can absolutely seed and leech without port forwarding, they will just have fewer connections than they would with port forwarding set up.

Do certain providers block uploading but allow downloading or something?

Not too late for PieFed to rename “communities” to “slices”