So Remote Buddy is an iOS app emulates keyboard and mouse clicks on your desktop I guess. And now you need those picked up by your player.
The best keyboard (and remote like Harmony) support comes in Plex Media Player. That’s not the app you’re using at the moment, which is Plex for Mac. If you use the former and put it into TV Mode, then it becomes an HTPC that’s designed for keyboards/remotes.
Furthermore, in TV Mode you can also custom map your key binds,
add or change audio and video filters at the ffmpeg level, lots of fun stuff.
Should the Plex for Mac app handle remote commands that emulate
Apple Media Keys? Yes probably that’s intended at some point.
But that app is very new, and PMP, however, is mature.