If you're using Powertoys Peek, it's not working with Opus, neither with any other file manager.
If you're using Quicklook or Seer, it should work (it does for me). Check if you have anything in opus binded to Space key (go to Settings > Customize >> Keyboard shortcuts and try to type Space in the Shortcuts search). Note that I have "Next image" for the viewer binded but since I'm not using the viewer often, it is working anyway.
For more information about Opus and Peek: