Best thing probably is to submit a case. You then can keep track of it in your profile and the people at Safe will get a notification.

Hi @davebarter​. I've checked with my colleagues who use MacOS and they can confirm experiencing the same issue in some versions of FME 2020. I'm sorry you've come across this! This seems to have been fixed in the latest build of FME 2021.

In your case, the date picker actually shows up behind the "Translation Parameter Values" dialog box. My colleague found that if you press and hold on the calendar below to keep viewing the calendar, whichever date you release the mouse on that date will be populated. Hope this helps!