That usually means something is supposed to happen after the login but for whatever reason the operation failed, times out and eventually the desktop starts.
This can be caused by a lot of different problems. Some error/warning should show up in the system log.
Before starting to reset configurations you could create a new user and quickly test if it happens there too. But checking the logs should be a good first step.
Created a new user. It too takes similarly large amount of time. Getting back from lock screen (not login screen) is instantaneous, for both old and new user.
Yeah, it arrives at the splash screen and sits there for a while. I scanned the journal and didn’t see anything in red, at least not that I can say that it is caused by.
Still faster then windows at least
I saw bug reports https://bugs.kde.org/show_bug.cgi?id=482082 where some users reported that this has been fixed after recent updates. I still have this issue after the update to Plasma 6.0.2. Can someone else share their experience?