I'm a pretty light user of GitHub, to be honest, and I don't understand 90% of the features, but having a remote backup to roll back to has saved me on a couple of occasions over the years, so I'm thankful for it.
I've always enjoyed the 'native Mac app' feel, and frankly it was one of the tools that opened up app design as a hobby for me back in 2014/15 (I couldn't stand Adobe UIs). These days most of the app is actually designed straight into code, since swiftUI usually makes visual iteration pretty quick. But any time I'm considered more sweeping changes, or designed app icons, I've used Sketch.