To always show the Menu Bar, even in full screen, go to System Settings > Menu Bar and set the option for Automatically hide and show the menu bar to Never.
More info: Change Menu Bar settings on Mac – Apple Support
Note that there have been many issues reported with Mission Control on macOS 27 Golden Gate, especially regarding the way Full Screen apps are handled. Some have been resolved by identifying and removing incompatible 3rd party extensions, others are bona fide bugs.
Have you rebooted your Mac? If not, that's the first step. If that does not help, then see if the problem is present when you boot in safe mode. That process performs some system cleanup and clears caches, and also disables 3rd party extensions that may cause problems.
Start up your Mac in safe mode - Apple Support
If that does not correct the issue, test in a new user account. A newly-created user account will have all settings at default, and if the issue does not occur in that new account then it provides guidance on what may need to be changed to correct the issue.
Add a user or group on Mac - Apple Support
Once the testing is complete, the new account can easily be deleted.
Delete a user or group on Mac – Apple Support
Those steps will help to isolate the problem.
It might help to download and run EtreCheck, written by a long-time forum member. The free version is fine. Post the full report using the Additional Text button. No personal information is revealed.
If the issue persists in safe mode and a new user account, that suggest that it's a bug that Apple needs to address. Bugs can be reported to Apple here:
Feedback - macOS - Apple
Reporting issues like this to Apple is the only way to get them fixed. They do prioritize bugs based on frequency of reports, so the more people who report it, the faster it will be addressed.
User level: Level 1 (4 points)
