Trying to upgrade to 6.6.0 from 6.2.0 in one shot unfortunately is not allowed…
so i downloaded 6.4.0 and gone ahead and installed that first.
Update took about an hour to complete to give you an estimate. Now i can finally take new snaps and go ahead with the upgrade to 6.6.0 which now agrees to upgrade!
this also took about an hour to complete maybe even a bit longer but be patient :). After this i tried to login with my domain account but it required the full SAMAccount name instead of just the name.
Checking if everything is ok and removing my snaps completes this long upgrade!