I would have assumed that connecting your PC to a hub built-in to your monitor then connecting keyboard and mice into the monitor would be a somewhat common configuration

I don't know; I tried this once (on a Dell U2715H), and the input from both the mouse and the keyboard got very jittery, to the point of making the computer very difficult to operate. I suppose there was some interference from processing and displaying HDMI signal; whatever it was, I decided not to bother with built-in display USB hubs.

I would guess hubs built into monitors to be tested with this exact use-case.

Heh funny I have a laptop connected to the USB hub in a relatively recent Fujitsu screen and then an old USB 2.0 hub connected to that one with keyboard and mouse connected to it. Works flawlessly. Guess I got lucky.

Most of my computing life the last decade is living off a laptop hooked up to a dock and a dinky little 4port usb2.0 hub plugged into that dock for webcam, mouse, keyboard, midi controller. It's pretty nice to just one cable my laptop into a desktop.