neowin[.]net/news/latest-windows-11-update-22000652-kb5012643-has-an-annoying-safe-mode-flickering-bug/
Microsoft released an optional Windows 11 update 22000.652 (KB5012643) a couple of days ago that added several changes and bug fixes including one that led to near-hour long startup delays. However, the update has apparently introduced a new bug to Windows 11 systems wherein there is flickering on the screen when one enters the Safe Mode.
Deskmodder has also provided a workaround wherein one has to choose 5 or F5 instead of 4 or F4 as apparently the problem seems to not occur when the network drivers are loaded as well.