I always had a dark cockpit at daytime. I saw the posts in " Insanely dark cockpit in daytime ". I tested it by changing the parameter "shadow details" in the rendering options from "3d on aircraft" (or higher) to "overlay" and my cockpit got brighter. This I tested in the "Set to medium" and in the "Set to high" configuration.
I disabled all plugins except Gizmo64. You can see the details of the graphic card and driver on the renderings screen of my Windows 10 64bit x-plane system.
Thanks for your help