2019 16" MBP
macOS 11.0.1
BTT v3.505 (1643)
Mission Control & Immediatley Show Desktop trigger does not show desktop. Mission Control activates, but desktops do not appear on top.
Tried it with keyboard shortcut and trackpad gestures, same result.
Same problem for me on Big Sur. It's working one time in two. I hope an update 
Same for me. Running a 2020 M1 MBA with Big Sur. Seems like when you have a window open already, it works most of the time (depending on where the cursor position is when you do the 4-finger swipe up) but when you don't have any window open, it doesn't seem to work much at all.
Would really love to see a fix for this. I think it's ridiculous that the desktops don't show up by default like they did when they first came out with Mission Control.
I started to have this issue after update to Big Sur.