I assume my default is Calibri as a blank document types in that (although that dialog only allows me to change the default, not see what it already is!) Is Calibri a rare font I didn't have before? I have a vague memory of selecting one of the few fonts which is variable spacing and also distinguishes between the number one, both cases of the letter eye, and both cases of the letter ell. It's amazing 95% of fonts have a few of those precisely the same! IiLl1 - they are all different in my browser, what do they look like to you?

Calibri has been available for a while. I think Win7.
However, I bet that update to Win11 is your source of problems. Try a Repair of your Office installation or go straight to Uninstall/Reinstall.