Experiencing the same on my RX 6900XT. Horrible GPU utilization and frames dropping way down below the 60fps mark. My old RX 5700XT worked just fine, and so does an RX 580 I've sitting around. It seems to be that the new Navi architecture does not play well with the game's engine. Ought to fix it before new Arma drops with the same issue which would be a disaster.