Provided are a method for performing wireless communication by a first device, and a device for supporting the method. The method may comprise: receiving, from a base station, information related to a physical uplink control channel (PUCCH) resource for reporting hybrid automatic repeat request (HARQ) feedback information and information related to a configured grant (CG) resource for sidelink (SL); generating ACK information, based on no physical sidelink control channel (PSCCH) transmission by the first device on the CG resource in a single period; and determining a priority value of the ACK information, wherein the priority value of the ACK information is same as a largest priority value among at least one possible priority value related to the CG resource.