Weren't they switching to a subscription model? I know they pushed back the release of this new version but apparently Spez didn't feel like giving more free API access in the meantime. Or maybe the Infinity devs gave up on Reddit. Who knows.
Infinity was one of the best mobile Reddit apps I've ever used. Now the only thing keeping me on Reddit still is the RES extension. When that will eventually stop working too or Reddit decides to get rid of old Reddit, I'll be deleting my account.
For me the subscription page opens when I open Infinity, so their probably rolling that out bit for bit. Don't know about the F-Droid though, might take longer till it comes up there as well.