OP-X PRO-3
is a plugin only and has no stand-alone application.
So it needs a live-host or sequencer to run, like e.g. Reaper, Ableton Live,
FL Studio, Cubase, Logic Pro, MainStage, Cantabile or GigPerformer to name a few popular ones.
In case you don't have a host or sequencer already or even are completely new to the world of virtual instruments this site lists a few
free or cheap hosts for simple playing or even more complex live playing setups.
Free or cheap hosts for simple playing or more complex setups:
Windows:
Hermann Seib SaviHost
This little free host lets you play OP-X PRO-3 like a stand-alone application
SaviHost Setup Guide
Cantabile Lite
This is a fully featured free live host which allows to combine several plugins or instances
https://www.cantabilesoftware.com/free-vst-host
Mac:
Apple MainStage
Fully featured professional live host for only $29
MainStage Setup Guide
Music Device Host
Almost free and M1 silicon compatible
https://www.mixagesoftware.com/#musicdevicehost
Protools users:
Since there's no AAX version you need a Meta-Plugin to use OP-X PRO-3 in Protools.
A Meta-Plugin comes itself in several formats including AAX and can load other plugin formats (including AU and VST3) inside itself.
Blue Cat Patchwork
Commercial and widly proven Meta-Plugin
https://www.bluecataudio.com/Products/Product_PatchWork/
Kushview Element
Almost free Meta-Plugin
https://kushview.net/element/
