One time payments are fine when you are in a growing market like iOS in 2009. The only long time successful Mac Indy app that I can think of without a subscription is BBedit which has been around since 1990 and made every transition along with Apple.
You find a new market and/or build a new product.
The solution to "oops we sold one to everyone we can think of" is to invent new kinds of value, not ways to extort existing paid customers.
Software especially with Apple and always needs maintenance. Should people expect free updates?
Most software, especially in the world of mobile/desktop apps are usually feature-complete. The problem is that developers keeps redesigning and refactoring them to justify development, rather than focusing on another product or marketing efforts.
Free bug fixes are generally expected. But nobody forbids you from releasing v2 and charging for it again (for example with upgrade discount).
Or more recently should users expect a free upgrade when Apple deprecated 32 bit apps?
The Mac sees a lot less churn than iOS. But things do happen that cause apps not to work there. The most recent is that Electron was using a private API and all apps that used that version of Electron on Macs broke.
Nobody forbids you from selling your software with an asterisk that says "works on X.Y version of MacOS, future releases will require a new license".
And if no one new is buying your product, I think you need to ask yourself whether you have a sustainable business or a hobby.
Bug fixes, yes. Other updates, no.
Sell upgrades, develop new products, etc.