It makes total sense, it just didn't occur to me, and I totally missed it in the docs. Thank you. It keeps crashing while looking for the feed, though. Perhaps my phone's specs are too low. I'll keep trying to solve it, since Feeder looks cool and promising.
You just need to prefix the npub with
nostr:-> see: https://github.com/spacecowboy/Feeder/pull/483/commits/95340d4b5ad7cf13cb740305c3ad1fb6b929a2c9