Fast User Switching option greyed out after deploying Login Window MDM Profile – Addigy

We have received reports from users stating that deploying a Login Window MDM profile on devices running macOS 11 or newer and including the Fast User Switching MDM key causes the Fast User Switching option to completely grey out in Settings, not allowing the adjustment on whether or not to show the Fast User Switching icon in the Control Center. This means if Fast User Switching is not already enabled before deploying the profile, Fast User Switching will not be enabled by the profile itself.

We have verified this issue through internal testing, and have filed an Apple Feedback to Apple with steps to reproduce the issue (FB12885798).

An article by Kevin M. Cox lists two currently undocumented MDM keys found in collaboration with the MacAdmins Slack, which seem to now control the Fast User Switching functionality in macOS 11 or newer:

UserSwitcher in com.apple.controlcenter, which now seems to control whether or not Fast User Switching is actually enabled system-wide.
userMenuExtraStyle in .GlobalPreferences, which controls how the Fast User Switching icon is displayed in the menu bar.

Note: This issue is only impacting macOS 11 or newer. Any devices running macOS 10.15 or older can continue to leverage the existing Fast User Switching option within the Login Window MDM profile without issue.

Workaround

In the article, Kevin provides an example MDM profile with the undocumented keys included in Raw XML hosted on GitHub, which can be deployed as a Custom Profile through Addigy.

In our internal testing, deploying Kevin's example MDM profile as a custom profile through Addigy has yielded a successful Fast User Switching deployment on macOS 11+ (Including Sonoma) using a Policy deployment and also a GoLive deployment leveraging either the user or device channel. Given the results of our internal tests, we can confidently recommend this as a temporary workaround.