That's strange because Iron is very similar to Chrome, and I am able to post questions/answers with Chrome 126.96.36.199 (just checked).
With Iron, I get redicted to the "Oops! Something Bad Happened!" - error page, where I am asked to report the problem to Meta if I think it's interesting.
I posted this issue here a few days before but the old question is gone. It might have been deleted due to 'being too localized', as someone told me.
If a user with an unusual browser gets to the error page, they should be told to use a supported browser instead of asking them to submit a bug report to Meta -- as this would just be a waste of time.