The issue of Exposè/Mission Control not working in Mac 10.15.2 can be fixed by applying a defaults write command. First, open Terminal app and type or copy the following command:
defaults write com.apple.dock mcx-expose-disabled -bool FALSE
After running this command, restart the OSX Dock by typing the following command in Terminal:
killall Dock
This will enable the Exposè/Mission Control feature and fix the issue.