As I've pointed out many times in the past, DLSS support is a joke, anyway, it's so sparse, it shouldn't be a serious consideration when choosing between NVIDIA and AMD; in fact, it shouldn't be a consideration at all.
If you're someone trying to gimp along at 4K with a card that can't actually handle that resolution, and your favorite game(s) that struggle(s) with this is supported, congratulations, you fit the probably 0.0001% of gamers who might find this crap useful. Yay. So now you're running a viable framerate at 4K (but not
really 4K).
Oh, and if your play type of choice is competitive online play? Forget about it. Upscaling adds intolerable latency.
NVIDIA's DLSS was introduced on February 15, 2019. Right now, not counting demos, there is still only 171 games that support DLSS (165 with DLSS 2.0+). A handful of those are VR games that nobody plays, too. That's a rate of 47 games added per year.
Meanwhile, AMD's FSR was introduced on June 22, 2021. Right now, there are 74 games with FSR support (though only 29 with FSR 2.0+ support). That's a rate of 56 games added per year. So they're outpacing NVIDIA.
https://www.pcgamingwiki.com/wiki/List_of_games_that_support_high-fidelity_upscaling
This is a tiny sliver of the total games out there. Steam adds about 8,000 PC games a year. So this barely covers more than half of a single percent of games added. It's a niche, irrelevant technology to nearly the entire landscape of games.
In theory, FSR is inferior, but you can decide for yourself how that shakes out with high-res screenshots:
Techspot: AMD FSR 2.0 vs. DLSS Performance in Deathloop