On the Mac there is not particularly a shortage of good photo/image editors, from affordable to expensive. Acorn, Pixelmator, Affinity Photo, Photoshop.
I’m not a professional and don’t want to learn Photoshop for ages. Also, oftentimes very basic ones are not sufficient, like most cheap ones from the AppStore. I haven’t found a proper substitute for this niche between super basic ones and Photoshop.
Pixelmator is what you want. Seriously. It's really good.
It's even one of the most sold apps in the app store. Can't miss to find it.