getframe pixel dimensions do not match figure position

When I use getframe.m, I expect it to produce an image that exactly matches what I see on screen. But getframe produces an image whose pixel dimensions do not match the size of the figure -- if the figure is on the built-in display of my laptop. If I move the figure to the external display (connected to my laptop), getframe produces an imge whose pixel dimensions do match the size of the figure. I'm running Matlab R2020b on MacOS 11.6.

How can I make getframe work as expected on my built-in display?

Example code:

>> figure; image
>> get(gcf,'position') % on built-in display

ans =

   677   160   560   420

>> snap = getframe(gcf); size(snap.cdata) % does not match!

ans =

         840        1120           3

>> get(gcf,'position') % on external display

ans =

         789        1074         560         420

>> snap = getframe(gcf); size(snap.cdata) % does match

ans =

   420   560     3