Uses SDL for rendering the UI. While it makes it work cross-platform it unfortunately means it won't look like a native application. Then again, I don't think there's a C library which provides cross-platform native UI, only the Lazarus toolkit for Free Pascal and WxWidgets for C++.
"Native" means compiled code (likely C/C++/Rust/Zig) for some. And it means using platform-specific UI widget for others. I don't care too much about the UI widget style as long as the implementation is good and responsive. I tend to use app in fullscreen (F11) with minimal chrome and to be honest I kind of like when each app has its own UI style, especially if it can be user-configured with themes. Apple/macOS users…
Mac users don't want all GUI apps to look alike; however, they should follow macOS UI/UX guidelines regarding copy/paste, drag and drop, keyboard conventions, etc. The whole point is to not have users having to relearn these basics for every new application.
Developers generally get these conventions "for free" by using the frameworks built-in to macOS. That doesn't prevent developers from creating custom, stylized interfaces if that's what's needed.
Even Apple's pro apps (Final Cut, Logic, etc.) look quite different from those that are bundled with macOS such as iMovie and Garageband.