I don't know about you, but I don't like the delay and how the screen jumps down when using the "Mission Control & Immediately Show Desktop Preview" action.
I was messing around the other day and found that macOS seems to render the desktop previews automatically if you invoke mission control while the mouse is in the menu bar.
So I created this sequence in BTT and assigned it to the 4-finger swipe up gesture (turning off the native gesture in trackpad preferences):
Note that the X coordinate of the move mouse step (2) is just somewhere near the (top) middle of my big monitor - it can be anywhere you want (in the menu bar).
Note also that the delay of 0.00 seconds (step 4) seemed to be necessary on my iMac. It may or may not be needed on other computers, or may need to add some actual delay.
This is working great for me and more or less back to the good old days of when macOS natively did this for you.
EDIT: since posting this I've noticed that there was some unreliability in the desktop previews being rendered with the delay of 0.00 seconds so I've now changed it to 0.10 seconds and it seems more reliable. I imagine the best value for the delay could be different depending on your CPU and/or GPU.