How locked down are desktop apps now on Mac, Windows and Linux? I haven't kept up. Do they still a lot of access by default to do malicious things with? I recently saw someone install the Adobe Acrobat desktop app and it installed its own extension inside of Chrome without asking. Games can have scary DRM as well.
Chrome extensions can't read/write to arbitrary places on your hard disk without asking for example and you can isolate them within separate profiles. Not saying they're perfect but there is robust sandboxing of what they're allowed to do. I'm curious how this compares to an Electron-based desktop app i.e. which is running Chrome on the inside but with the standard restrictions Chrome places on tabs and extensions unlocked.
It’s hit or miss. There have been advancements on macOS and Linux where there are mobile-style permissions and sandboxing in some cases, but one needs to be aware of how apps are packaged to be able to leverage these advancements. Adobe stuff and Chrome on macOS for example have basically free reign still as they have specifically opted out of OS sandboxing, while a lot of small indie apps are sandboxed. Chrome I think can be put in a sandbox on Linux by way of Flatpak.
Windows has done practically nothing and is the same as it’s always been where desktop apps can do basically whatever they please, especially if given privileges with UAC (which seemingly every other Windows app needs for some reason).
Mac App Store apps are (mostly) sandboxed. Developer ID signed Mac apps distributed outside the App Store are mostly not sandboxed.
The tooling is often better there too, e.g. one can keep a short leash on app network activity with Little Snitch and similar but I’m not aware of an equivalent for browser extensions.
Of course risks exist with desktop apps too, but historically this kind of buy-and-exfiltrate scheme is comparatively rare with desktop apps, particularly on macOS where signed apps are sandboxed and can’t do a whole lot without user permissions.