Old android phones used to emulate a USB mass storage device when you would connect them. To the computer, the phone would appear as a usb stick. Modern android phones, on the other hand, use a protocol called MTP (Mobile Transfer Protocol), which is completely its own thing.
The reason they switched to MTP is that the old approach gave the computer complete control over the phone’s storage; the phone would become completely unusable while connected in this way, and would just display a “connected via usb” splash screen. With MTP, the phone continues to be usable while connected via USB. But it has the downside that MTP is a much less widespread protocol than USB mass storage. On personal computers it should “just work”, but on stuff like printers it might not.
Personally, I think they should bring back USB mass storage emulation as an optional feature. Heck, it can still be done, but you need to compile your own android ROM with usb mass storage drivers, which I’m not nearly skilled enough to do.