This is either trivially easy or not possible, and I can't tell which after tracking down about a dozen Q&A posts here, GitHub issues, or other random google sources. (Sorry for the tone of exasperation...)
If it matters, I'm working on a Button. One answer I saw was to change rectscale. This DOES change the font size in the editor, but does NOT change font size in my running game. I can tell by print(mybutton.rect_scale) that my change "sticks". Other threads offer other solutions but these all seem to involve custom fonts even when the question was "without loading custom fonts".
I realize I may want a custom font someday. But I'm just prototyping ideas now.
If the answer really is "not possible", I would greatly appreciate a tip on where to find one without entering the malware storm that threatens when I google "free font".