To allow nicer transitions between the Plymouth start screen and lightdm, I created a custom theme that fades in the login screen nicely. I cannot, however, detect, if the greeter was started because the system started, or because I logged out and returned to the login screen. There, however, I should probably fade from a black background instead. Export to the greeter whether it is shown because of system startup or because of the user logged out and returned ot the start screen (and probably because I created a new session to login as another user). Reproducible: Always
There is a property to show if the session is acting as a lock-screen. (mostly for Ubuntu where they use LightDM for session-locking) That /might/ help for session-switching but not logging out. I don't have access to whether we started due to log-out or session start. I can try and discuss this upstream. I guess it should be fairly easy to do, but I have to get it through their first then update the backend and both sets of client libraries. Don't count on it soon :)
We no longer use lightDM, having moved to SDDM several years ago. As such, this bug report is no longer applicable. Bugs reports for the new SDDM-based login screen should be filed to one of two places: 1. Visual/UI bugs with the login screen UI itself, or feature requests: plasmashell | Theme - Breeze 2. Bugs with the login/user switching process: https://github.com/sddm/sddm/issues