My guess that's since by default Excel 2016 opens each new workbook in the same instance. If you start new instance for the second workbook it works - rename without Enter and clicking in same workbook, go on second one, return back on first and we sheet keeps new name.
We fought so hard for this feature over the past. And that is the reason why I raised the question "works as designed" or faulty behavior? Problably nobody paid attention when they changed the document Interface. And of course I admit the described way is not a way everyone works every day. xD
Since today I have problem to change the name of the table sheets. Each time I select Tableau1 (have a french version) and type a name it returns immediately to Tab1. Impossible even to type some precision after Tab1. Very uncomfortable as I use always my own name of sheets in formula,, dynamic table etc..
Is there something to check in the "preferences" or elsewhere?
My version :Excel in Office for Mac 2016 (student and family) Version 16.21.1 (190123)
I am afraid the software maybe corrupted (it has a year) bought in Microsoft online store.