Mail preferences screen size can't be modified; green button missing

When using FULL SCREEN Mode in most applications the Green Button as well as the Yellow and Red Button will disappear

To get them back, just Mouse Over the Top Left of the screen will make the 3 buttons including the Green to reappear.

First image is Full Screen of Safari

Second image is Mouse Over Top Left of screen

The link below is related to Full Screen Mode of Mail but same would apply to most other applications

link >>>> Use Mail full screen on Mac

The other method to Exit Full Screen mode is to use the ESC key on keyboard

The Mail preferences window does not have a green button; I don't think it ever did.

It also is not resizable, but I have seen at times problems like this, where the window, for some reason, becomes the wrong size.

You could try temporarily changing the screen resolution and see if it makes the window into a reasonable size.

Good catch and I missed the Preference aspect 😔