Sort of! On Windows, it's WebView2, which is more or less Chromium. On Mac it's the system's Safari, which I'm pretty sure is frozen at the OS release (or maybe gets updated with OS updates). So I'm less worried that it'll break with an update, but I've had to fix a few issues when someone is running on macOS 10.13 or something like that, where Safari is just missing some modern JS thing. I've solved that with polyfills and Babel and it's been alright.
CSS is the other issue, where old Safari doesn't support grid and some other stuff. So I stick to flexbox and well-supported stuff.
On macOS, Safari releases are independent of OS releases and show up as separate updates as and when they’re released. They may coincide on the date sometimes. It’s not like iOS where Safari updates never show up as separate updates, and are bundled with iOS updates.
Do you happen to know if the WKWebView always uses the latest Safari that's been installed? That's been the thing I'm uncertain about, where I think I've run into situations where the installed Safari should support some JS thing, but Recut doesn't actually have access to it, and I've suspected that WKWebView is just frozen at whatever the OS came with.
I don't really see how is that a problem. Webapps work pretty well despite the fact we have a bunch of different browsers – why the Tauri situation should be any different?
With Electron you know exactly which version of the browser engine you are using.