There was a bug some time ago dealing with the same thing:
Anyway with a 4090 you may want to go TAA + frame generation. It´s better for quality and the card will not suffer at all under TAA. I even use it with 125% scaling as anything above 100% activates the supersampling, resulting in better looking antialias. As you are running a lower native resolution than me it will even hurt less your performance. DLSS involves a performance boost but based on a quality reduction. I don´t think is intended for the 4090, even if it´s still possible.
Cheers