Hi Roy, thanks for posting here in the Microsoft community, Error 0x80070306 often points to a corrupted system file or driver conflict.
Since you've tried multiple steps already, I suggest running DISM and SFC tools to repair system files, simply open Command Prompt as Administrator then run this command: DISM /Online /Cleanup-Image /RestoreHealth and sfc /scannow
After that, try the update again. If it still fails, consider using the Windows 11 Installation Assistant https://www.microsoft.com/en-us/software-download/windows11 or Media Creation Tool for a manual upgrade. https://www.microsoft.com/en-us/software-download/windows11
I hope this helps you out, let me know.
Chard