It doesn’t seem like Piefed is available to login on many of the popular Lemmy mobile apps.
Why is that?
PieFed uses a different app, which is still in early stages. See https://piefed.social/post/484755
Those apps are not compatible with PieFed.
If you try with your reddit credentials you’ll see that it doesn’t work either, nor does it with your gmail account or mastodon account.
Those apps are only compatible with the Lemmy API. PieFes doesn’t have a API yet.
Piefed is compatible with Lemmy in the sense that a Piefed server can talk to a Lemmy server using ActivityPub, but they are different software beyond that, and so they have different APIs at the user level.
It’s not really different from how Mastodon is different software, even though Mastodon users can see and reply to Lemmy posts.
In addition to what the other comments mentioned, PieFed has a number of features that Lemmy lacks - like Categories of Communities, hashtags, the initial wizard to sign you up to communities that you are interested in, showing the community side-bar text alongside every post in it, unique messages offered irt particular instances or news sources, etc.
It will take some time to get an existing app to catch up to all of those, when Lemmy lacks those features entirely.
deleted by creator
An app is available now, for testing: https://piefed.social/post/484755
Awesome! I’ll be giving it a go soon, thanks!