Why does my Universal Control on my keyboard and mouse stop when I use my iMac M1 as an external monitor for my M4 Macbook Air (main display)?

Why does my Universal Control on my keyboard and mouse stop when I use my iMac M1 as an external monitor for my M4 Macbook Air (main display)?

I set up Universal Control for my iMac and Macbook's keyboard and mouse. They work seamlessly, but once I try using my Macbook as a main display, and my iMac as the external display - my iMac's keyboard and mouse stop working. The mouse will move, but I'm unable to click anything - and my keyboard won't work. Only the Macbook's keyboard and mouse work on both screens.

What does work is if I use my iMac as the main display and the Macbook as the external display. Then, BOTH the mouse and keyboard for the iMac and Macbook work seamlessly! This is what I want, but i want my iMac to be the external display and Macbook to be the main display (the graphics are better).

I updated both systems and restarted, unchecked all settings, etc.

I called Apple Support and the tech verified that I was taking all the steps that I can, it's just the software that won't allow it. Maybe there will be an update?

Is there any one else that has run into this issue and found a workaround?

Thanks.