Setting Fast User Switching has been broken since macOS 11. e.g. if MultipleSessionEnabled is specified at all in a profile the behavior is always false. This has been problematic for some MDM customers because some MDM vendors include this value as part of more broad login or restrictions profiles. The customer has no option to NOT include the value if they want to configure other settings. I have had an Applecare Enterprise Case open on this behavior for 2 years. Apple acknowledges the bug but I'd guess it affects such a small number of customers there's no engineering resource being assigned for resolution.