Hi Lee. In exactly the same situation, 2016 Pro new PC (have working happily on older desktop, but want to see if can get on to a new windows 11 PC) I can confirm 2016 has run fine on my windows 11 desktop for over a year, although this was installed as win 10 and upgraded.

I believe that if you activated your existing installation "online" then there is no validation key to be found in the  "qbregestration.dat" file.

Every post just tells us what we already know.

I did manage to get a "validation key" out of intuit "online Quickbooks" phone support yesterday, tried it with support person still on phone, didn't work.

I really just want a working version so I can access over 20 years of historical data, any thoughts appreciated.

Paul