My dxdiag says Miracast is available, but not finding a wireless device?

I read an article that said, to find out if you can cast from your PC to a TCL Roku TV, you can run dxdiag, and there should be a line that says "Miracast: Available, with HDCP"

My dxdiag says Miracast: Available, with HDCP, but yet in File Explorer when I right click on a .mp4 file, Cast To Device, it says, "No Device Found"

Is there something special that I need, in order to cast to my TCL Roku TV?  My PC uses an ethernet cable to get internet.

Do I need to have a wireless USB dongle for internet on my PC if I want to cast to my TCL Roku TV?  I don't know what I'm missing, but my TV doesn't see my PC, and my PC doesn't see my TV.