Undervoltage circuit lockout for XBee2

Minimum operating voltage of an Xbee3 is 2.1V.
Do we need a UVLO circuit if voltage falls below 2.1V ?
If voltage falls below 2.1V, does that bricks the Xbee3 modules ?

Yes, you should have some sort of UVLO circuit where the module is powered off if VCC drops below VMin.

It is unknown what could happen if the modules VCC drops below VMin.