JCE,

do I need to do anything special to have my GPU detected/enabled?

I have an AMD Radeon R7 200 I believe.

XMRig detects it but after a few jobs all counters remain 0 or N/A so I wanted to give your GPU version a try.

Edit: this shows XMRig for my card...

[2018-06-23 22:19:09] compiling code and initializing GPUs. This will take a while...
[2018-06-23 22:19:11] #0, GPU #0 AMD Radeon R7 200 Series, intensity: 576 (8/256), cu: 6

not a top class card but the extra 120H/s is better than nothing at all