mail program Settings screen is stretched to four screens wide

I was making some changes to my mail Signatures a couple of months ago and suddenly the Mail Settings screen stretched out to be four screens wide. I cannot shrink it back to its original size. There are no controls to do so.

There is no problem with the Mail Settings screen when I log into my second account on this same laptop.

It is the standard width, that you cannot change.

I am using a 2013 MacBook Pro running Ventura, 13.6.7

Where can I find the .plist file that controls the width of the Mail Settings screen ?

I am hoping that if I can edit it to match the one in my other account, then I can fix this problem.