How do I mirror a specific window to a projector on iMac Pro?

Hi all,

I have an iMac connected to an Extron projector, and it works fine for displaying one window. However, as a teacher, I want to keep instructions or videos displayed while grading or planning without losing sight of the window on my Mac. Currently, I can only see the projected window on the projector, not on my iMac, which is inconvenient if I need to pause or adjust the video. Is there a way to project just one window to the projector while still viewing it on my Mac?

[Re-Titled by Moderator]