A ttk::button -style Toolbutton (which has existed for a long time) can have
arbitrary width and height.  A plain ttk::button, which is realized as a macOS
Push Button, can have arbitrary width but fixed height.  (Actually the height of
the ttk::button does increase, but the white rounded rectangle is always drawn
with the same height, vertically centered in the bounding box of the
ttk::button.)

In the mac_styles branch there is a -style GradientButton which can have
arbitrary width and height, and the same is true of -style ImageButton.

This sort of thing is a job for the programmer, and the Tk geometry managers
provide lots of tools to allow the programmer to do it easily.  Tk does not know
enough about what the programmer is trying to do for any one-size-fits-all
automated scheme to work.  Possibly there could be a magnification operation
which changes the pixel size per window.  But I think that should be handled
by the window manager, not by Tk.