Assuming you have a Gsync/VRR monitor, certified/ultimate doesn't matter
First and foremost you need HW GPU scheduling ON in Windows,
I recommend the latest drivers game-ready drivers(or at-lest the ones that were release for for the game you want to play)
You need to disable any FPS caps, ingame, external, NVCPL, RTSS/Afterburner, etc.
Turn Gsync ON Window/Fullscreenn or just Fullscreen in NVCPL, like normal
Now you need to force Vsync on in NVCPL, I recommend applying on a per game base in DLSS3 games so it doesn't mess with other games.
Now you ready to play DLSS3 games.
A couple of FAQ I see everywhere
Why you need Vsync forced on NVCPL?
-> With FG on a 4090 some games excess 144fps, spider-man can reach 250+, so you need Vsync ON so Gsync can act properly in its refresh windows and game doesn't tear.
Why games vsync option gets greyed out or dont work with FG on?
-> When FG launched vsync wasn't officially supported so games greyed it out, a couple of drivers later nvidia now supports Vsync in the control panel but games aren't yet up to speed and so most if not all disables Vsync in its options or dont apply it correctly.
Why disable FPS caps? The gospel says you need 2-3 bellow your refresh Rate
-> DLSS3 frame generation works in conjunction with Reflex to lower latency, reflex already lowers you cap below the max refresh rate, for 144hz it shows 138.
Why should I use DLSS3 if Iam already happy with the framerate?
-> Its up to you ofc. With FG you can get alot of more FPS if your GPU was already hitting ~144fps or a fps you were happy with, it will now work consume less power and thus saving you money, or you can turn settings you had previously lowered or RT, or you can disable DLSS2 super resolution for Native resolution and turn on DLSAA. It also helps also FPS fluctuations
Latency?
Its subjective to each other. I know there is latency but to me it doesn't affect so far in the games I played I prefer 10x to play a game at close to max refresh rate rather than <100fps. My opinion is for SP games I dont play competitive and Iam not young anymore