https://vk.com/video382662960_456239323
Landscape is flickering on the horizon when Lumen is the lighting system and SkyLight is the lighting source (and camera is not above the scene, but in the place it is in the game).
did you ever solve this by chance?
I heard they fixed flickering with software lumen raytracing in one of the latest ue5 releases, but there was no way to fix it in that release, and my info about fixing is not confirmed.
As a probable workaround, I surrounded my map with mountains.