I have a 3090 Ti and it can use DLSS 3. So can your 3090.
DLSS 3.0 has three components:
- DLAA / Super Resolution
- Ray Reconstruction
- Frame Generation
The first two are supported in 20xx-series, 30xx-series, and 40xx-series nVidia cards. You need a 40xx-series card to get the 3rd option.
Even if we can’t do Frame Gen, I recommend using DLSS Swapper to upgrading to DLSS 3.7.10.
I also recommend installing nVidia Profile Inspector and configuring it following this video. Be careful with this. Do not change any settings other than the ones he specifically mentions.