AFIK...
You need to download and install the SDRPlay API. (Instructions on their strange website, in the downoads section.)
Then recompile the SoapySDR stuff to include the SDRPlay API details, and install that where GQRX can find it. (Instructions on the spam ridden pothous SDR site.)
I did (eventually) manage to get all that working* with an earlier Linux OS, not re attempted it with the current OS, yet.
(* But with slowly increasing recovered audio latency.)
73.
Dave.
If it aint broke, hit it harder.