It just has a button that says "Active Blender Denoiser"
The RPR manual infers there are there supposed to be Denoising options in the RenderLayer panel.
Correct. On macOS we switched recently to use the Blender built in denoiser (see release notes) https://www.amd.com/en/support/kb/release-notes/rn-prorender-blender-v2-2-blender-2-80-2-81
Blender 2.81 provides a denoiser node which is in fact the same library as our CPU ML denoiser, so on macOS we use this instead. Users can enable this in the View Layer properties, with the button marked "Enable Blender Denoiser". Other OS's use the RPR GPU denoiser (for speed), but there is no GPU AI denoiser on macOS.