Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Thanks Gloria, when you do those actions, have you checked that the spelling language of the relevant content elements have actually changed? (in PPT on Windows: select element, Review, Language, Proofing Language).
Because I have also observed that it sometimes temporarily stops highlighting the spelling mistakes dynamically when you do changes like that. But, it doesn't actually change the language settings of the content box, so the spelling mistake highlighting will return later. Because it is still set at the wrong language.
I posted here because I was hoping/expecting for some sort of override switch to this behavior that I just hadn't found. But even if that wasn't possible, I thank you for all the help trying to solve this. If you have contacts with Office product team, please request they consider making Office suitable for use in international companies ;)