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.
The issue was first brought to attention by German outlet Deskmodder which noticed the problem. Others like XanxoGaming, that posted the early Ryzen 7 5800X3D review, also noted the issue:
Windows 11 KB5012643 (April). I'd avoid it for now. Entering W11 Safe mode made me enter a non-stop loop of blinking help window, rendering W11 safe mode UNSAFE. Uninstalling it fixed it.— XanxoGaming (@xanxogaming) April 28, 2022
Config: 12900K + DDR5 + RTX 3080...
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.
In the known issues list of the release, Microsoft hasn't mentioned this bug which could mean that the company is unaware of the problem. So for now, if you are someone who has to use the Safe Mode for some reason, it may be best to avoid this optional Windows 11 update.