This has taken me a long time to figure out, but there is something wrong with Display Fusion when I am using the Unreal Engine Editor- essentially the behavior will be that the engine window doesn't respond. Mind you, I've crashed that editor plenty, and I can tell the difference. The behavior is things like not being able to right click in a blueprint window to access prompts, or navigating across a BP window by dragging the mouse across (while holding a key)

I couldn't figured out what this was until I started closing display fusion and noticing the problem just didn't happen. Later this made me pay attention where the moment I encountered an issue, I would close Display Fusion and see immediately resolution. I know the Unreal editor does funky things with its dockable windows and in my case, I was using multimonitor profiles for custome windows, but it happens even if I'm not using multimonitor profiles and just using the native window setups.

I have to use the Editor, but I am huge fan of Display fusion, and I loved being able to hit a key on my streamdeck to cycle a DF profile to rearrange all my assets perfectly with my monitor.