Mac pop up notifications getting cut off on the right

Solution 1:

From comments… based on nothing but guesswork, try the old "switch it off then on again" with a slight twist.

Try changing monitor resolution temporarily, maybe also reboot after you change it. Leave the external disconnected whilst testing.

Solution 2:

if you're connected to an external monitor, go to displays in the setting menu and click the arrangement tab. Once in your arrangement tab; drag the white bar from your mac to the external monitor screen. then move it back to your mac. it fixes the mac trying to decide the width of the screen. I run into this bug every so often. The white bar indicates which monitor to display the notifications and it's defaulted to your mac. This accomplishes what turning it on and off again would do without actually turning it off and on again