Thanks to CyberFSR, courtesy of PotatoOfDoom, I found out that both mine 980TI and 1080TI are capable to run FSR2 on some DLSS2 supported games.
So, I've built the drop-in DLL to take advantage of FSR2 @ 1280x720 internal resolution over DLSS2.
Currently getting great result with 1080P on those two older NVIDIA graphics adapter.
These are the KNOW TO WORK games that I was able to test by checking the internal resolution with reshade:
The Ascent
Horizon Zero Dawn
Death Stranding
Marvel's Spider-Man Remastered
Marvel's Guardians of the Galaxy
No Man's Sky
Forged In Shadow Torch
Cyberpunk 2077

DLSS2FSR (CyberFSR)
Thanks to CyberFSR, courtesy of PotatoOfDoom, I found out that both mine 980TI and 1080TI are capable to run FSR2 on some DLSS2 supported games. So,...

DLSS2FSR GP (CyberFSR) Pre-release
General purpose FSR2 drop-in for DLSS21.
Built for 472.12 standard driver compatibility & the 900/1000 series.
This build is currently limited to Nvidia video cards where the game/launcher does not implement internally any hardware test to lock the DLSS2 support under the RTX feature level. ↩
Releases · noInk/CyberFSR2
Unofficial FidelityFx Super Resolution 2.1 drop-in for DLSS2 - noInk/CyberFSR2