Save/Don't Save Menus No Longer Respond to Tab and Spacebar (post Big Sur)

Prior to Big Sur (OS 11.1), I could use tab to move between the options (buttons) in the type of pop-up menu shown in the image, and spacebar to select an option. For example, in the menu here I could a) press spacebar and have this email 'Save' and b) use tab to transition the highlighted option to 'Don't Save'.

Now, neither of these work, which I don't like bcs. I prefer to use the keyboard. I can't seem to find an option to reenable them (or work around the issue). Any ideas?

Solution 1:

Have you checked whether following in System Preferences > Keyboard > Shortcuts is selected: