Enable or Disable F8 Advanced Boot Options in Windows 10  

Brink, my point was that, because the Startup repair operation does not take it upon itself to run when I use Standard mode, probably it is something else, not Startup repair, that hangs "Please wait" as reported. Indeed there is no need for Startup repair to run, nor for an installation, because all OS boot items work, in both modes.

Regardless whether displaybootmenu value is present or not in BCD record, whether its set to Yes or No, my dual boot Windows 11 + 11 system always shows Legacy Boot Menu at every reboot, despite Bootmenupolicy for each OS is set to Standard. I think it happens because initially the 2nd OS was installed from ISO mounted in the 1st OS booted. So the 1st OS shows Modern bootmenu with dual boot options. I added BCD store also to the 2nd OS drive upon booting to it with bcdboot, but when OS boots from it as primary in BIOS, only Legacy boot menu is shown.

I tried Repair Install from Windows Update to fix that, but it failed with generic error likely some device driver related. I don't want to do any other install type, since 3rd party apps will be deleted. So: how do I revert to Modern Boot Menu on the 2nd drive? May be a Reg key will do the trick? For example, on Windows Server the Legacy menu is default option, can't change that with any published bcdedit commands, so its likely overriden by a Reg key.

Also, is there a Tutorial to find out what caused Repair Install to fail? I looked at CBS log, nothing specific in it, DISM and SFC show no errors.