Update Install Error: EFI Partition

Laptop: HP Elitbook DragonFly
Installed OS version: Windows 11 23H2

Error Description

System Settings → Windows Update: system tries to install the update version 22H2, even though a higher version of the update has already been installed.
Error Message: “This PC doesn't meet Windows 11 system requirements. We couldn't update the system reserved partition”. Install error 0xc1900201

Possible cause of the problem

Windows Update Feature doesn’t have enough space on the EFI partition.

Solution

1. Run PowerShell or cmd as Admin

2. Monting EFI-partition as Y volume: mountvol Y: /s

3. Switching to the fonts loader folder: Set-Location Y:\EFI\Microsoft\Boot\Fonts

4. Making the backup of fonts on C:
   New-Item -ItemType Directory -Path C:\EFI_Fonts_Backup -Force Copy-Item * C:\EFI_Fonts_Backup

5. Cleaning fonts from EFI to free space: Remove-Item * -Force

6. Unmounting EFI on C drive:
   Set-Location C: mountvol Y: /d

7. Restart OS → Repeat attempt to install updates → Success

What I’ve learnt when solving this problem

1. Error code 0xc1900201, or any statement about “system partition” in Windows 11, indicates that the system partition in the pre-boot environment is too small or full to install the update, often due to old font files.

2. Discovered how Windows OS is booting on UEFI:
   - UEFI reads EFI partition → starts bootmgfw.efi
   - It loads BCD and starts Windows

3. Discovered EFI structure
   EFI
   ├─ Microsoft
   │ └─ Boot
   │ ├─ bootmgfw.efi ← loader │ ├─ BCD ← boot configuration │ ├─ ... and .efi │ └─ Fonts ← lots of .ttf/.fon files ├─ Boot
   └─ may contain some folders from HP, antivirus, etc.

4. Article that helped me

5. Book which I’d like to read: Mark Russinovich “Windows Internal”.