I followed these instructions from @wiedehopf to install PiAware and Airspy on my RPi 4;
Installing Raspbian Buster Lite on the Pi4 isn’t an issue, download the image, put it on the sd-card, enable ssh access, and plug it in.
Oh the WiFi setup is a bit different if it’s required, but not a problem either.
Following that you just install the piaware stuff: PiAware - dump1090 ADS-B integration with FlightAware - FlightAware
Then you run airspy-conf and you are done with the setup: https://github.com/wiedehopf/airspy-conf#airspy-conf
From your description, you may have missed the airspy-config portion