Lock screen still showing when I unlock my S25 Ultra

This issue is part of the new lock screen redesign in One UI 8. The dynamic clock and overlay sometimes fail to refresh when you unlock.

You should try to clear cache partition:

Power off your device and when you turn it back on, old Volume Up + Power, then select Wipe cache partition.

If that does not work, go to Settings > Lock screen > Clock style and switch to a different style, then switch it back again.

This forces the UI to reload the lock screen renderer.