A long shot, you could try add_filter( 'show_admin_bar', '__return_false', PHP_INT_MAX );, which would override any other hooks that could be interfering.

Failing all of that, your theme or a plugin could be interfering. Try using the Twentytwenty theme and deactivating all plugins. Deactivate any must use plugins by renaming the /mu-plugins/ folder. Unchecking the option in your profile should now work. Restore your normal configuration, one module at a time to narrow down the cause of the problem.