stuck at 60hz

Hallo, This is more of a what do you think this could be than anything. I've got an RTX 3060 & an old BenQ xl270z 144hz monitor. A few weeks ago I had driver corruption and a faulty DP cable (or so I thought...maybe it wasn't) at the same time. Used DDU and got a new DP 1.4 cable, took some...