Threema?

Also sideloading has been around as a term for a long as smartphones have existed

What? Where did you get that from?

If you take the iPhone as the first smartphone, those weren’t even supposed to have natively installed apps by third parties but just use websites for everything. You could install third party apps before that on symbian. You could always install apps on android. So no, the term neither has been around as long as smartphones nor is it ubiquitous.

“Sideloading” is only relevant to Apple devices as no other platform is as locked down as ios, so the word isn’t even used outside that context. For other devices, you simply “install” applications. That’s it.

There’s also threema which is pretty tried and tested and quite popular where I live (and also not connected to weird crypto schemes) but it of course has the same issue.

But “<” means “less than”…?