Hags has to be on, otherwise you won’t get Frame Generation. For best results for the 4090, you want to have DX12, HAGS on, and DLSS Frame Generation on. Don’t confuse this with DLSS3. You don’t want that. You want TAA and Frame Generation.
I have a Pimax Crystal, and my VR settings are on ultra.
Also, here are my NVIDIA control panel settings: