(I used to use an app called CornerClick for years to do this, but it no longer works in modern macOS)
CornerClick would let you simply CLICK on one of the screens corners (with NO modifier key) to trigger things like Mission Control, Show All Windows, Show All Application Windows, Show Desktop, etc, etc.
No other app lets you do this.
Is there any way you can add this feature to BetterTouchTool? Somebody already requested this feature five years ago, but his thread didn't get any responses.