[---] in the case of Word (I tried making Calibrí 11 regular as the default font in "all documents based on the normal template," and what happened next time I created a new document? Aptos!).
In Word for Windows, setting a new default font for future documents based on a template is a fully functioning option. It is working just fine here (running Word, Microsoft 365 business subscription, version 2406, Windows 11).
Since it fails for you, something is preventing you from saving changes to the Normal template.
That "something" could be different things. If you are in a corporate environment, maybe IT support has decided to delete your Normal template regularly which would get rid of the changes.