Please see the video. When operating in the UE viewport, if the cursor conceptually moves outside of UE, left-clicking at this time will not accidentally click on other programs. However, the middle mouse wheel (scroll wheel) can still affect other programs, resulting in simultaneous operation of both UE and other applications, which is undesirable. Is there a way to avoid this? Is this a UE issue or a system issue? Can it be fixed?
I was able to reproduce this behavior, and it appears to be driven by a Windows setting rather than a UE-specific issue.
On Windows, the mouse wheel can scroll inactive windows when you hover over them, even if they don’t have focus. To prevent this, please disable:
Settings → Bluetooth & devices → Mouse → Scroll inactive windows when I hover over them.
After turning this off, only the Unreal Editor receives the scroll wheel input, and the other application no longer scrolls while you’re operating in the UE viewport.
Please let me know if this resolves the issue on your side.