I've downloaded the experimental build and now it works. I still don't know if there is a way to install RPR for both B3D 1.79b and 1.80.
The experimental "Nightly" build of 2.80 is not code signed the same as the RC1 build is.
Unfortunately, as you correctly point out the Brecht version and the subsequent official RC1 build for macOS still do not fix the problem for v2.0.94 of RPR.
I get the same error as you.
There is one known way around this issue.... disable SIP on macOS. However... that is not really advisable but it does prove this is a code signing issue at Blender's end.
Today I quickly tried the BRC 3 and again RPR 2.0.94 it didn't work (same problem as above), then I downloaded the experimental Blender build and it worked. If the final Blender release is going to be like the RC I think it's a problem for RPR.