They wrote their own GUI toolkit (oof) and it's hardware accelerated (argh), so OS portability is going to be unusually difficult unless they planned for it from the beginning. No mention of that in the article, so I doubt they did.
They already have very experimental Linux support. You have to build whole app yourself though. I'd say that in month or two we'll get a binary.
You can track Linux porting progress in this issue
I mean on the one hand, the hardware acceleration is awesome. The GUI toolkit is not of course (I assume MacOS has a default one to make everything look like it belongs?), but at least they made it look like a native app instead of the usual electron shit where it's clearly a web page with a window border and some design 15y old me might think is cool but 16y old me would already have been ashamed of.
As I understand, GUI toolkits will usually support various widget styles or "Look and Feels".
So, they can just use a glossy graphic for a button on macOS and a flat graphic on Windows 11, without having to reimplement the whole application in the native toolkit. It will usually not feel entirely native, but at least, it won't look out of place...