Didn’t mean to dig this up from the grave, but I wanted to include a bit more info for anyone else dealing with flickering lights.
I’m using UE5 with lumen, and there’s a glass material in my project that’s been flickering when it reacts with a directional light casting from behind it (representing sunlight through a window). After going through numerous fixes of anti-aliasing, increasing final gather quality, using ray trace shadows, etc… it turns out the solution posted above works!
Many of the glass tutorials online recommend using a Lighting Mode of Surface TranclucencyVolume. Setting it to Surface ForwardShading fixed the issue.
Hope this helps anyone else deep in Google-fu.