SOLVED (I think): In project settings, I unchecked occlusion culling, and the flickering stopped.
Cesium / Google 3d tiles constantly flickering regardless of lighting setup. Have tried with Cesium sun, dynamic lights (when bright enough), etc… flickering stops only when there is no light source (completely dark)
UE 5.3.2
Cesium installed from launcher
windows 10
i5 10400f
rtx 3060