I had a heck of a time upgrading my Windows 11 Pro System from 23H2 to 25H2 and I really did not want to do a clean install. I really shouldn't have had a problem but it was; the issue had to do with Hyper-V and Windows Subsystem for Linux.
My system is an AMD Ryzen 9 with all the bells and whistles, and it was constantly failing windows update where the error was 0x800f0991.
Running DISM & SFC did not help at all with the results displaying everything was fine with the system. Booting from USB and trying an offline scan also proved to be useless.
I do a lot of work with Hyper-V and upgrading from 21h2 to 23H2 was painless which is why I was so puzzled why I couldn't go from 23H2 to 25H2. I figured it had to be something with windows virtualization; it was the only thing it could be. I have a number of 3rd party software installed a game or two but with the changes in Hyper-V, the network virtualization stack, it made the most sense that was going to be the best place to start.
So I backed up my VM's exporting them before removing Hyper-V. I had to remove Data Center Bridging, Hyper-V, Virtual Machine Platform, Windows Hypervisor, and Windows Subsystem for Linux.
Before removing the virtualization components in windows it failed the 6 times when I tried to upgrade though a booted USB and PC Health Check.
Now that I'm updated to Windows 11 25H2; unfortunately Hyper-V will not work and causes a continuous boot loop. However the upgrade to 25H2 from 23H2 worked very well so long as Hyper-V was removed.
