I'm with other people here. Make this a one-time purchase. If a major macOS update requires significant changes to keep the program working, make that a new version that people need to buy. A pretty standard way to keep people from feeling screwed if the break happens right after they bought your software is to give them the next version of your software for free if you release it within 1 year of their purchase.

I think you're actually likely to make more money that way because people will pass on adding yet another subscription to the pile they have already.