Updating to iPadOS 15 Unknown error occurred (1100) 065B.044C

I've been trying many times to update my iPad Air 2 to iPadOS 15 but all attempts was unsuccessful, but didn't make the device unusable. The tip was then to update it from my MacBook Pro running macOS Big Sur 11.6 by connecting the iPad to it. I was able to download the software and then attempted to update the iPad. The update process started and after about 80% of the process I got Unknown error occurred (6). 068B.0006. I tried a second time and got Unknown error occurred (1100) 065B.044C. The third time I got the same error code. The problem is that the device is left unusable. It seems like the only way forward is to restore it to factory settings, and that is not an option for me.

Please advice!

Len