a few devices/companies have tried this (not Apple obviously):

Motorola Atrix: https://en.wikipedia.org/wiki/Motorola_Atrix_4G#Accessories

Microsft Display Dock (Windows Continuum): https://en.wikipedia.org/wiki/Microsoft_Display_Dock https://www.microsoft.com/en-ca/windows/continuum

NexDock: https://nexdock.com/

Samsung DeX: https://en.wikipedia.org/wiki/Samsung_DeX

Apparently Android 10 has a desktop mode as well