Polytonic Greek keyboard for MacOS

I'm taking a class in Biblical Greek and am struggling with using accents with Greek Polytonic keyboard. I would expect long pressing an h would provide accent, grave, umlaut, iota subscript, etc. But it only gives the accent.

I was trying to input "thi" (the dative case of the definite article) with accents and subscript, ie τῇ. I finally figured out that I needed to type "t[{h" in order to produce the desired characters with accents. It is hardly intuitive.

So I hoping to find either an alternative on-screen keyboard for the Mac (I've tried agk from the iPad, doesn't work) or a cheat sheet or assistive keyboard or any other options to make this easier. I can't be the only one struggling with this. So if you have a solution, what works for you?

Thanks in advance.