Quite often, an in-place upgrade from Windows 10 to Windows 11 — or even a repair-style in-place upgrade within the same Windows version — fails because of an EFI partition that boots cleanly but is actually corrupted.
That problem usually only becomes visible during the upgrade attempt. Setup then works around it with unclear messages on the screen and in the logs, without identifying the real culprit: the state of the EFI partition.
[For both the EFI and Windows RE partitions, there is also the more advanced case beyond the basic procedure. This comes up, for example, when the partition is located in the wrong place in the partition order and therefore cannot be enlarged, even though a Windows update requires more space in the partition. A later post will cover that part.]
tl;dr
Quick steps to recreate the EFI partiton.
Important notes
Use list disk to identify the correct disk, because it is often Disk 0, but not always. Use list vol to identify the EFI partition; it is usually 100 MB or 260 MB, GPT, and formatted as FAT32. Make sure the correct volume is selected before formatting it.
The drive letter U: is only an example; any free drive letter will do. The bcdboot command assumes that C:\Windows is the correct Windows installation path in the recovery environment, so verify that first.
Boot Windows RE from the ISO image, go to Troubleshoot > Command Prompt, and then run:
diskpart
list disk
select disk 0
list vol
select vol 3
format fs=fat32 quick
assign letter=U:
exit
bcdboot C:\Windows /l en-en /s U: /f UEFI
