I seem to have lost the auto-login facility - using Tumbleweed latest snaphot 11112021 Plasma KDE.
I have checked the Yast Setting and that still shows auto-login enabled. Have also checked the behaviour setting in System Settings / Start Up And Shut Down / Login Screen (SDDM) and that looks right too.
The setting in the file in etc / sysconfig / displaymanager is
That’s how I recalled it some years back, but DISPLAYMANAGER_AUTOLOGIN entry in /etc/sysconfig/displaymanager is what counts now. I don’t usually enable autologin, but testing here with openSUSE Leap 15.3, and KDE Plasma 5.23.3, it works when I assign the autologin user via YaST.
After a bit more playing around I discovered that the ‘lost auto login’ issue is due to the latest version of ‘suse-prime’. If i remove this package or install an earlier version of the rpm, auto login works again (although with a raft of error messages on booting).
I will play about a bit more and then submit a bug report.