We tried this Global Preference configuration profile payload to enable fast switching in the device, but unfortunately, after successfully applying the payload, fast user switching still remains disabled in the device with the user restricted to modify the setting. PFA the screenshot of the settings applied in the Profile as well as a screenshot of Login Window settings.
OS version: macOS 12.1
<dict>
<key>PayloadVersion</key>
<integer>1</integer>
<key>PayloadUUID</key>
<string>7b3041b6-d1fb-43d8-af8c-1028cde8b534</string>
<key>PayloadType</key>
<string>.GlobalPreferences</string>
<key>PayloadOrganization</key>
<string>MDM</string>
<key>PayloadIdentifier</key>
<string>7b3041b6-d1fb-43d8-af8c-1028cde8b534</string>
<key>PayloadDisplayName</key>
<string>Mac Global Preference payload</string>
<key>MultipleSessionEnabled</key>
<true/>
<key>LULookupDisabled</key>
<false/>
<key>com.apple.autologout.AutoLogOutDelay</key>
<integer>0</integer>
</dict>