npub15l94g7dqqvvwelnwqer5vu7v4jt237kl5p7q4kygdt67hqry4y0sus9qz5 (npub15l9โฆ9qz5) https://bugzilla.opensuse.org/show_bug.cgi?id=1221461#c12 - the reason is that nextcloud fails to open kwallet. If the wallet is open, it works.
Looks like a rough edge with Plasma6 for the moment. I also hope for a fix soon.