It is possible nowadays: I’m hosting quite a few services on an 5 years old Android. Just with Termux, no root required. Of course connectef it’s just to the internal network due to all the security concerns mentioned in the post.
To solve all the bandwidth/connection issues, I’ve bought a usbc-ethernet dongle that works like a charm.
To mitigate battery issues I’ve limited the charging to 85%.
I would never host Jellyfin there, but with webdav and Kodi I can get my media served easily to all my devices at home