There is no green button in the settings window. That is not anything new in Ventura.
It seems that the window is indeed not resizable, too. That would not be a problem, except that yours is apparently too big.
At this point, the only thing I can suggest is to try resetting the preferences (this does not affect your accounts or messages).
Quit Mail.
In Finder, press Command-Shift-G and paste
~/Library/Preferences/com.apple.mail.plist
Drag the file out of the folder and place it, for example, on your Desktop.
Start Mail again. A new plist file is created automatically.
Does the preferences window now look normal?
(if not, you may put the old plist file back)