It seems Supabase only supports JS and PL/pgSQL, not Python or the rest of PG languages. But still you could use compile-to-js languages like ClojureScript.
Unfortunately python for Postgres is only available as an untrusted language extension, which can provide avenues for things like privilege escalation[0]
We’ve decided to only bundle trusted language extensions so that there is a balance between flexibility when it comes to users writing their own procedures, all while maintaining security.
I've written a fair bit of pl/pgsql for my startup.. not exactly my frst choice of langauge but I've turned to it for certain optomizations in or system. definitly NOT the choice I'd make for most situations. the language is incredibly clumsy and there isn't much material out there to learn it well. a lot of the ps/pgsl i know comes from reading code and guessing how things should work.
We’ve decided to only bundle trusted language extensions so that there is a balance between flexibility when it comes to users writing their own procedures, all while maintaining security.
[0] https://www.postgresql.org/docs/current/plpython.html