Hi Thorgils.
Thank you for your reply. I have understood that you are having issues with SetupDiag, answers to questions in this regard are not within the scope of our community support, you can post this question on Microsoft Learn, where a more specialized support person will be able to answer your query.
In the meantime, you can refer to the following link to enter safe mode
Start your PC in safe mode in Windows - Microsoft Support
In safe mode, try to remove the problematic driver by following the steps below
1 Search for "Command Prompt" in the taskbar, right-click it, and select Run as administrator.
2 Enter the following command, note: here oem65.inf driver as an example, please change it to the problematic driver, and then press the Enter button
pnputil /delete-driver oem65.inf
See if you can upgrade to Windows 11 properly after uninstalling all your problematic drivers.
Additionally, you can get the update log by following the steps below.
You will need Explorer's address bar and type in
$Windows.~BT\Sources\Panther
This path is a hidden folder, so if you can't see it, set Show hidden files in Explorer. Locate the file named setupact.log and open it with Notepad or another text editor.
Since this log file is large, you may need to be patient until the file opens.
Once it opens, search for 0xc0000409 from the bottom up until you begin to see the Windows error 0xc0000409, which will be accompanied by the cause of the error. If you are not sure what is affected, please upload the log file to OneDrive and send it to us.
Share OneDrive files and folders - Microsoft Support
If you're not using OneDrive, let me know and I'll start a private message with you where you can upload the issue to me.
Best regards,
Zev - MSFT | Microsoft Community Support Specialist