A: Indirectly, yes. Games built specifically for SM 6.5 (like Cyberpunk 2077 with Path Tracing or Avatar: Frontiers of Pandora ) can render more efficiently, but installing the driver won't magically boost old games.
Introduced with DirectX 12 Ultimate, Shader Model 6.5 is the standard that allows developers to use advanced GPU features. The headline features include: Shader Model 6.5 Download
Revolutionary ways to handle complex geometry. A: Indirectly, yes