I was using the Legacy Raspbian 32bit on my RPi 3. It could not determine what the OS was until I manually changed the /etc/os-release file to replace all occurences of Raspbian with Debian so it would select apt as the package manager .. then halfway through apt hung up and never completed .. tried again .. same issue .. hangs when it updates man-db database.. no furthur testing was done cuz I gave up lol