You can do things with ADB (like copy files, etc). In fact, ScrCpy uses it for remote control.
You do have to enable developer options, then USB debugging, physically connect to a pc and authorize it (also enable permanent authorization and disable timeouts), etc. (I may forget a step or two there).
I wouldn’t really consider it a native sharing system - as you said, it’s not enabled by default, and it’s a bit cumbersome. It’s a debugging utility that happens to enable remote debugging which can be used for other things with a bit of work. Not something I’d tell most people to use, because it’s cumbersome, and opens a security hole. It’s also a bit unstable. It tends to drop the network connection for no apparent reason.
I use it to setup phones, because I can script a handful of app installs with it, or unlock the bootloader and flash a rom (or root the device).