Good eye and no, you won’t find that particular MIDI FX setting in the current version of Scaler.
Scaler is providing the chords but as Davide notes, the sounds are coming from Native Instruments Electric Sunburst instrument. If I had to wager, I would bet that the MIDI FX item shown in the dropdown is either a new name for the existing NONE sound setting (which would make since) or a dev build with some other midi routing piece.
Either way, if you have a good Metal instrument, you can use Scaler to drive it.
Interesting. I did not know Scaler had a separate “Midi FX version”.
When I apply Scaler as a Midi Effect, which I’ve done for years, I use the straight Scaler VST (not Scaler Audio) and there is no change in the Sound dropdown options.
In my case I’m on Windows and the DAW that supports Midi Effects natively is Roland ZenBeats. When you use Scaler to apply midi effects in DAWS that don’t support MIDI FX natively (like Studio One or Ableton (and as @jamieh points out most of the others) it must be routed manually where the instrument “listens” to the Scaler track.
In my experience it is a straight forward process (once you know what you DAW needs) but not as easy as just applying an FX .