1. Open Windows Powershell or Command line as Administrator
Start -> Powershell -> Runs as Administrator
2. Open Diskpart
diskpart
3. Identify the EFI partition showing up in Explorer
list volume
4. Select the EFI partition (Replace ‚X‘ with the correct drive letter):
select volume X
5. Remove the EFI partition’s drive letter (Replace ‚X‘ with the correct drive letter):
remove letter=X
6. Exit Diskpart
exit
7. Open RegEdit
Start -> Type „regedit“
8. Find the right key/folder
Computer\HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
9. If the EFI partitions drive letter is still in registry, delete the value.
For example: \DosDevices\X:
10. Close RegEdit and reboot.
source: https://answers.microsoft.com/en-us/windows/forum/all/window-10-efi-system-partition-and-recovery/e7389cec-f0a3-4f85-bc7e-8b22be22680b