Verify the version of the following MSISCSI driver on the system:
c:\windows\system32\drivers\msiscsi.sys
The version that will expose this behavior is 6.3.9600.18624 for Windows Server 2012 R2 and version 10.0.14393.1066 for Windows Server 2016.
So, I decided to step back and do an in-place upgrade. I obtained en_windows_10_enterprise_2016_ltsb_x64_dvd_9059483.iso and reinstalled it clean. It accepted the license key and activated it without any problems, so we can assume the key itself is good.
Download Zip https://urluss.com/2yVzop
Then I launched the en-us_windows_10_enterprise_ltsc_2021_x64_dvd_d289cf96.iso installer from within Windows. I opted for a clean install removing personal data and applications. Was it wrong? Should I keep them to ensure the activation upgrade? Anyway, the install process worked almost till 70%, and then it suddenly popped up a small message box with the text: "Windows 10 installation has failed". No error code, nothing.
The system is indeed on Windows-Version 1607. But this is "normal" for the Long-term Servicing Branch (LTSB, see i.e. -windows/faq-windows-10-ltsb-explained.html ) and actually it's the most recent version. So to say "my system is up-to-date". It's the same version of Windows that run on ATMs and Ticket Machines etc.
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