Pretty recent, I check it every once in a while to see what’s going on. Of course, with macOS generally most of the changes happen around WWDC ;)
SwiftUI on macOS is currently ok for a few usecases. One is little document apps. Emphasis on little, this is going to be things that wrap an image or a text file or something. The API is reactive so it’s not really designed for complex/partial file formats. Another good usecase is just pure drawing/animation. This code will look identical on macOS and iOS and is very easy to write with SwiftUI. Finally, the last thing that mostly works is just lists of content. Not table views, those aren’t very good yet. I’m talking about Twitter-like content, as in a media viewer in list form.
What doesn’t work well is anything that has to do with controls (either they look very ugly, the control doesn’t exist, or SwiftUI has no concept of some significant portion of the control). If you want to do like focus loops or right clicks or anything complicated, forget it. (Some of these are getting fixed piecemeal, but AppKit has like a thousand little things that make good apps and it’ll be a while before they are all fixed.)
By way of example, I actually have some small apps that show this off well. https://github.com/saagarjha/EffectivePower is a little view-only document shoebox style app. It’s 100% SwiftUI, has one main screen that is a hand-drawn graph, and some auxiliary UI. This makes it about as good as it could be for using the framework. Making the graph was a delight. Making it perform well was a little bit of work but not too bad. The document abstraction mostly works except SwiftUI expects me to be able to create new documents and I’m just a viewer app so I need to crash if you try to make a new document. The sidebar is a List, which is fine, but I actually wanted it to be a Table. However Table selection asserts right now if you update its selection faster than the NSTableView that backs it animated. Of course in SwiftUI there is no concept of animation duration so you can’t really stop this from happening. You can also zoom the graph in the app. On Monterey if you tried to zoom a couple of times the system magnification gesture just stopped working silently. On Ventura I believe they have fixed this, or at least it isn’t trivially broken anymore. This is common for SwiftUI.
By way of contrast, https://github.com/saagarjha/VirtualApple is also pretty simple but it’s 100% AppKit. I had originally written it in SwiftUI but it’s just not possible to make it be a good Mac citizen. It is “document based” but because it deals with multi-gigabyte VMs I can’t actually let it do the default document based behavior, which includes making hidden revisions whenever the files update (which means you get a dozen secret copies of the VM). In AppKit I can just turn this all off and still look identical to any other system app. (Caveat: if I want the recent files menu and don’t want to use a storyboard, this is actually not available even in AppKit without SPI). Also, I have a little configuration screen which is all buttons and checkboxes. AppKit lets me align it precisely how I want so it looks nice. In SwiftUI it would look pretty awful.