I will assume that you are using a higher DPI setting, which is where I
notice the problem. Unfortunately, an application developer can specify that
a dialog or window is not resizable, in which case there is nothing you can
do about it if you are using a different DPI setting that makes the dialog
boundaries they determined no longer work for you. In this case, you have a
rather ugly workaround: they keyboard. Just press tab and you'll move to the
next control (whether you can see it or not) and then you can just hit the
space bar to press the button. Alternately, just hitting return will
activate the default button, which is typically the OK button.