“Setting up your Mac…” at every login (10.15.5)

Question

Every time I log into my Mac, I see the desktop/dock, then the "Setting up your Mac" screen appears over the top of the desktop. After a few seconds, previously launched applications start and can be used as usual, but the "Setting up..." screen remains and covers the desktop.

Additionally (and possibly related?), the set of application that re-opens at login appears fixed and is not affected by ticking/unticking the "reopen applications at login" box on the logout/restart confirmation popup.

This issue doesn't present itself when I start in safe mode.

Based on OSX 10.13.4 'Sets up your Mac' every login, I attempted to uninstall my anti-virus software (Eset endpoint security), but this had no impact on the issue.

I also tried creating the file /private/var/db/.AppleSetupDone as mentioned in How to stop Setup Assistant from showing up on every restart on Mac Mini with OS X Mavericks?

I'm fairly sure that some 3rd party software is causing this issue, as reinstalling OSX resolves the issue, however I'd like to find out what the real problem is.

Is there anything else I can check/try?

Answer 1

Following jaume's comment, I checked my login items (https://support.apple.com/guide/mac-help/mac-a-blue-screen-startup-problems-mh21210/mac).

It turns out that Setup Assistant had ended up in there, and was impossible to quit once opened. Removing it from Login Items and rebooting solved the issue.