There were many issues reported with Mission Control and Spaces on macOS 27 Golden Gate 27.0 and 27.0.1, especially regarding the way Full Screen apps and app switching are handled. Some were resolved by identifying and removing incompatible 3rd party extensions, others were bona fide bugs. The recent point update, macOS 27.2, appears to have addressed the more significant issues, including full screen app switching and moving grouped applications.
If you are still experiencing specific issues, then bugs should be reported to Apple here:
Feedback - macOS - Apple
Since safe mode 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 suggests that it's a bug that Apple needs to address.
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.
Since updating to macOS 27, keyboard navigation inside Mission Control no longer works.
Control Up Arrow enters Mission Control, and Control Right/Left Arrow switch between Spaces.
From what version of macOS did you update? I have a second Mac on my desk that is running macOS Tahoe 26.7.1, and the behavior that you describe —using unmodified arrow keys to switch active windows in Mission Control— does not work. Moreover, I just checked on my son's Mac that is still running macOS 15 Sequoia and the result there is the same. The unmodified arrow keys have no action in Mission Control on macOS 26 or macOS 27. Nor is such action documented by Apple:
View open windows and spaces in Mission Control on Mac - Apple Support
Mac keyboard shortcuts - Apple Support
In other words, I can reproduce the 'issue' you describe, but that appears to be the expected behavior with default settings, at least on the current versions of macOS Golden Gate, Tahoe and even Sequoia.
