Provided are a method by which a first device performs wireless communication, and a device for supporting same are provided. The method can comprise the steps of: receiving information related to a sidelink (SL) bandwidth part (BWP); receiving, from a network, SL synchronization priority order information set through global navigation satellite systems (GNSS)-based synchronization; receiving, from the network, information for indicating whether selection of a base station (BS)-related synchronization reference is disabled; detecting, on the basis of the information for indicating that the selection of the base station-related synchronization reference is disabled, a synchronization signal transmitted through the SL BWP by a GNSS-related synchronization reference or other UEs; and performing synchronization with respect to the GNSS-related synchronization reference or one synchronization reference from among the other UEs on the basis of the synchronization signal.