help F3 and mission control not working

Can you check in System Preferences and see if the Mission Control settings still look correct?

Do you have another account that you can try and log into and see if the same thing happens? Use the Users & Groups System Preferences pane to create another one and then logout and login into the new user and see if still a problem. If it doesn't happen, would suspect a corrupted plist file in the original account.

Another thing to try is do a safe boot -- hold down the Shift key during start up -- does that change behavior?

Good luck...

Does it open if you double-click on the app?

It's in the Applications folder.

Mission Control and Launcher both not working under Catalina. Neither the keys nor the icons will start the apps. Reporting to apple.com/feedback

How did you "fix" it?

Good luck...