Can't update Windows 11 25H2 security update

Hi Wilson, thanks for posting in the Microsoft community, the error you're seeing 0x80070306 usually means there's a problem with Windows Update components or system files after a manual ISO upgrade, what you can try.

First, Run Windows Update troubleshooter, simply go to Settings > System > Troubleshoot > Other troubleshooters after that Run Windows Update.

Then Reset Windows Update Components, Open Command Prompt as Admin, Run these one by one:

net stop wuauserv

net stop bits

ren C:\Windows\SoftwareDistribution SoftwareDistribution.old

ren C:\Windows\System32\catroot2 catroot2.old

net start wuauserv

net start bits

Also, Use DISM and SFC to Repair System Files,In Command Prompt simply run as Admin then type this:

DISM /Online /Cleanup-Image /RestoreHealth and sfc /scannow

You can also Download Update Manually https://www.catalog.update.microsoft.com/Search.aspx?q=KB5070773+ simply Go to Microsoft Update Catalog, Search for KB5070773 then Download and install the correct version for your system.

Also, you can use In-Place Repair, if all else fails, re-run the ISO upgrade but choose “Keep apps and files” to repair Windows without losing data, optional only.

I hope this helps you out.

Chard