Two more firmwares (Google TV - Android 11) were successfully flashed to 65P815 with panel ST6451D02-3 - R166 and V254 (local update by renaming it to R167 instead of V254 after flashing R166). I find V254 colour not as good as R166 and so flashed it back to R166 after trying it for a short while.
More details of firmwares from here.
More details of firmwares from here.