There is a Reddit post in r/AncientGreek which shows how to customise the Mac Keyboard, "MacOS Polytonic Greek Keyboard Customisation tips for learning to touch type Ancient Greek". This is useful if one wants to remove keys to save on-screen realestate. My on-screen keyboard just has the diacritics (accents).
Good question! When you’re in the Greek keyboard on your Mac, hold the shift key then press the [/{ key next to the “p” key. This will give you the iota subscript. Then release the shift key and simply hit the same [/{ key as before for the circumflex. Then hit the vowel you need and you’ll have both the iota subscript and circumflex with the vowel. If you toggle on “show keyboard viewer” you be able to see the whole keyboard. You can then play around with the shift and option keys to see different forms. Hope that all makes sense and helps!!
