Provided are a method for performing, by a first device, wireless communication, and an apparatus for supporting same. The method may comprise the steps of: receiving, from a second device, one or more sidelink synchronization signal blocks (S-SSBs) including a sidelink primary synchronization signal (S-PSS), a sidelink secondary synchronization signal (S-SSS), and a physical sidelink broadcast channel (PSBCH); obtaining an average reference signal received power (RSRP) value for at least one S-SSB from among the one or more S-SSBs; and determining, on the basis of the average RSRP value, whether to select the second device as a synchronization reference.