This is half-true.

Windows and macOS both make it difficult to install self-signed (or unsigned) software. For example, I made http://www.lofi.rocks (an open source Electron-based music player) and I'm not going to spend like a few hundred bucks a year to have a non-self-signed cert. This makes both macOS and Windows complain when users install the app. More draconian practices (that "protect users from themselves") will make it even harder for independent open source devs like me to share cool projects with a wide audience.