DIAGNOSIS Yes, normal. The Core Lighting RGB ring and the 240Hz panel generate significant heat. The upper rear casing is a heatsink.
FIX Ensure proper ventilation. Leave at least 4 inches of clear space around the rear vents. Do not mount it flush against a wall. Turn off the Core Lighting in the OSD (System → Core Lighting) if you are concerned. This reduces heat slightly.
IF THAT DIDN'T WORK If the heat is excessive and the screen shows artifacts or shuts off, that is a failure. For normal hot-to-the-warm-touch operation, there is no fix. It is the design.
HEADS UP This heat can accelerate dust buildup inside. Use compressed air to blow dust out of the rear vents every few months. Do this with the monitor off and unplugged.