Sideloading implies you have to jailbreak, like an iPhone. I could sideload apps on my iPhone if I really wanted to, via sidestore. I just don't have any use for that (and the better options are paid).

With Android, Linux, macOS, or Windows, it's just installing. I use Macs, virtually no Mac users care about the Mac App Store. It's trash. We don't like it, we don't use it. It's not on my Dock. It's in the Apple Menu and can't be removed from there. So I ignore it. Once in a while I look, see it's still trash, and ⌘+Q that shit. If apps are signed by Apple, installing is as easy as (install wizards) or easier than (drag app icon on Applications shortcut) Windows. Of course 'brew install' via the terminal is even better since it bypasses Apple's gatekeeper service (or can be made to, I forget). Windows it's a bit less static (no gatekeeper) but more spyware/malware threats. And then there's Linux. With Android, it's more like macOS where you gotta deal with a gatekeeper, but it's easy enough to deal with... for now. (To be clear, easier than macOS outside of 'brew', but not as easy as Windows/Linux.)