Let's say I have a button widget of arbitrary size,

is there a conventional way to make its text to fit or let's say
resize in proportion of the button's new size?

If so what is it?
No, there is nothing built-in. You can probably make it work, but tkinter is designed to work the other way around: you specify the text and the widget will automatically resize to fit.
Is there a conventional, simple way to make the fontsize of text option in a widget to fit?