I downloaded quartus prime, and it said to download and install device support, so I did, choosing MAX II/V. But when I run Quartus and try to create a project, it says you must have device support installed. When I check the device installer, it says MAX II/V is already installed.
Have you tried to restart your Quartus? The Quartus need to restart after the device support has been installed or the device may not be reflected in the Quartus.
Try to install the latest Quartus lite version 20.1 to check whether the issue still persists.