Having this same issue. A workaround that just worked for me was to:
Open System Preferences
Click on Displays
If not already selected, select Scaled under Resolution:
Choose a different scaling from the one that you current have selected
Switch back to your preferred scaling
If previously on Default for display, re-select that option
Once I switched back to Default (in my case), Mission Control started working as expected.
For reference, I'm running macOS Big Sur 11.4 (20F71) on a 2019 MacBook Pro 16 with a Radeon 5500M GPU. I haven't updated to 11.5.x yet because I use this laptop for DJing and upgrading is hit or miss for support with my mixer and DJ software.
Hope this helps someone.
Cheers,
Flux aka Andy
Topic:
App & System Services
SubTopic:
Core OS
Tags: