I first noticed this in older version and then tried v1.18.1 in a test instance.   Chrome (Windows 10) and Safari (iPadOS) exhibit the issue.  However with Firefox (Windows 10), I can create a ticket.

I added *.domain.com to allow System iFrame in settings.  Without this, I don't even see the welcome to the support center page as expected.

Creating tickets without iFrame works ok with the problem browsers.

I was hoping that this seemingly browser specific issue was because my production instance of OSTA was old. 

I made minimal changes to OSTA - just the System iFrame thing.

Any ideas on how to troubleshoot this issue further?