I don't think he's the one with the bounty. But, @greenart7c3 has a pull request for the app ID issue that I opened. I think retrnull is not interested in maintaining garnet, just like you said I think he wanted to release a proof of concept.

@greenart7c3 would you be willing to complete all the bounties at https://bounties.monero.social/posts/147/garnet-maintenance-sync-upstream-new-icons-resolve-amethyst-dual-install-conflict-etc create a release on your fork of garnet and collect the bounty? I don't think retrnull is going to merge PRs. You'd wind up taking up maintenance but it would be something you'd pick up some xmr for, especially since youre on nostr, I bet you'd get tons of Monero tips too that retrnull would be getting if he had a nostr profile. It looks to me like the hardest part is going to be sync with upstream amethyst. 

Don't forget to change the xmr donation address in your fork if you decide to do it.