Interesting. I have this problem too. I suspect it's due to having a high-resolution / HiDPI screen, which is using a scaling factor for drawing most windows/etc. I thought it might be a Linux issue, so I wasn't really worried about it, but it sounds like it's affecting some Windows machines too, so I should probably try to look into it and see if there's a way to fix our textbook author's graphics library.
One workaround for me is just to make all of the font sizes be half as big, but then the fonts will all look too small on someone else's computer!
To help me debug this, can you run the following commands in Thonny, and paste back what it prints, as a comment?
import tkinter as tk
root = tk.Tk()
font = tk.font.Font(family="Courier",size=100,weight="normal")
Also, what is your screen resolution ("Display Settings" under the Windows settings/control panel)? Also, under the "Display Settings", do you see anything about "Scale" or "Scaling"/ If so, is it 100% or something else?