it turned out to be the pop-up blocker!
I tried on a Windows computer which did not have them enabled and it worked. I then verified that Chrome and Safari on the Mac were actually blocking pop-ups which is always recommended anyway, but I have now added a site exception for Intuit.
Just a thought, but you guys should make it so that no pop-ups are necessary, that would reduce the friction a bit?
Many thanks for your detailed suggestions!