efi

How To Repair Broken EFI Partition

Assign both your Windows partition and your EFI partition a drive letter.  The EFI partition by default is not assigned a drive letter, but you can use diskpart to assign a letter temporarily.  Then make sure you know which drive letter each partition is assigned in the environment you’re using. When you’ve got both partitions assigned a drive letter and you know which partition has which drive letter, modify the example command below as needed.  In the command below, the EFI partition is X: and the Windows partition is C.  Change those as needed for your setup:

C:\Windows\System32\bcdboot C:\Windows /s X:

That will cause the EFI bootloader files from your Windows partition to be copied onto your EFI partition, which should get it working.

If it doesn’t work, try formatting your EFI partition as FAT32 just to erase it and start from scratch, then try running that command again.  Again, that command is what Windows Setup runs when it first installs Windows in order to set up the EFI partition, so it should be able to get you a working EFI partition again.