I agree with high friction sideloading. it is the best of both worlds. no friction sideloading is too easily exploited by scammers. having a member of my family exposed to this kind of thing in the past taught me some things.
I don't agree with the word "sideloading" though. It's just _installing_.
"Sideloading" doesn't refer to the installation process, but to the file transfer process. You're sideloading when you transfer, e.g. APKs from your notebook to your Android. Or, from a USB stick into your phone or something.
In general, though, "sideloading" also refers to any "non-app-store" installation. It's a kind of colloquial shorthand. It's not really a technical term. But it's adequate for getting the point across.
If you just called it "installing" without qualifying it, how would anyone know that it's a different process, or that it's accomplished not by navigating to the app store? It seems that you would invite ambiguity here!