I received a file from a friend to render in my PC, I thought that Cycles would use my RX 5500 XT to render it, yet seems it doesnt. Under Windows it is listed as a recognized device, under Linux not even that. The rendering process takes about 10 minutes, so I guess it is using y CPU because I made a test here at my job, using a GTX 980 and it renders the image in 1 minute and 31 seconds. So, still Cycles cant properly use OpenCL with AMD cards? I have gogled about it but cant find a definitive answer.
Under Edit > preferences > System > Open CL
your video card should be listed. If not > update driver. When loading foreign files you should click “Load UI” away.
My card is listed. In Windows, at least (it is not listed in Linux) and I have it selected.
I believe theres a separate driver for the OpenCL support you have to install under linux. Alas I haven’t used linux in a decade so not sure which driver exactly. You are probably better off asking in the respective online community for your specific linux distribution.