Since Big Sur the text alignment for standard dialogs on macOS is centered, but we found a way to adjust that if needed:
For FileMaker , you can use the new Dialog.SetTextAlignment function to change alignment.
In both cases you can pass left, center and right as desired wish. You can also ask for natural alignment, which may do right or left depending on the locale. Also defined is the justified value, but not sure if the dialog honors it.
You can try those in MBS FileMaker Plugin 12.1pr6 of our plugin or newer.