I don't believe the 27" 2017 "non pro iMac" has a T2 chip. I believe it's the iMac Pro, and 2018 MacBook Pro, possibly the 2017 MacBook Pro as well, (I'd have to check again.)
I have a late 2015 27" iMac (main computer), and a late 2013 13" MBP (I used for the beta process)
I haven't had any issues beyond the usual upgrade issues, and for me they were minimal, and easily fixed.
I am working with the developer of one thing, that has minor issues, but nothing critical. Even during the beta process I had very minimal issues. The developers of my programs did a really good job this year getting things ready.
I would be inclined to agree with Robin here, not saying there haven't been issues, but I'm not seeing them more widespread. In Fact, when I googled, the main results pointed to the apple communities, and only a few results.
I would think, if it was really "as bad as people say it is" I. would see more widespread results.
I'm an Op on Freenode in the #MacOSX channel, I usually go by MacinMan, or iFrog, but am not able to change my name here for whatever reason, after I created it several years ago. Anyway, I haven't heard a lot of gripes and complaints from users there, and there are many developers, IT professionals, even one or 2 Apple support people, and I've seen the most noise from these threads.