I‘d be happy to pay for an upgrade if future macOS changes break the functionality of this - cool - app, which would require the creator to update it. More work

I‘d be happy to pay for an upgrade if future macOS changes break the functionality of this - cool - app, which would require the creator to update it. More work, which I would pay for. But not a subscription, sorry! Plus, I‘d prefer to (but that’s impossible?) install via the App Store, to avoid a black box.