So sorry to hear of this; you would have thought you’d be done with this by now….
I am not qualified to give you any clear advice as to how to proceed forward but I do see the dilemma: Wait for the PSA to increase to the point of becoming visible on PSMA - or go back on ADT to slow it down but by doing so you may NEVER visualize it on a scan. The first scenario is chancy because it could metastasize or spread further….the second puts you on ADT, possibly for life. What do your DRS say?