Printing
My phone isn’t giving options for 4x6 to print photos. Just says Letter.
iPhone 11 Pro Max, iOS 14
That would depend on the settings for your printer. See if you find any documentation about settings to go with AirPrint. I do not see any settings on my iPhone when I attempt to print a photo that are any different than printing an email, except for double sided printing. I have an auto duplexer for multi-page documents.