Depends on EXACTLY what is going on
OBS Studio composites video sources... meaning if you have a PowerPoint window (I use Windowed Slide vs Full screen .. but same principles apply) then you can NOT generally interact with the application in the OBS Studio preview window (any more than you can interact with TV characters on TV screen).... [OBS Browser being primary exception, and I think there are others... but in general you do NOT interact with applications via the OBS Studio screen.
In my case, I use Windows Slide show, with the window partially available, which lets me mouse over the slide deck, NOT make the Slide Show an active window (this has specific technical meaning), and I can use my mouse scroll wheel to adjust slides FWD and back
