When I add my account instead of browsing lemmy.ml as guest, the button will simply grey out and nothing will happen. This has worked for me in the past.
I have the same problem
I have the same problem as well, and I have tried to contact the dev via Matrix, but no reply so far…
I can say we pinged the dev a week before this 0.12.0 update, which had some api changes, but didn’t hear anything back.
Native iOS Client to Lemmy.