I started this post, when at the time I had a 3080 with only 10GB and definitely short on VRAM.
I’ve then switched to a 4090, which yes is a dream of a GPU, but not worth the cost, as most of the time I was limited by the CPU (5800 X3D).
So I returned it and got an used 3090, which is been more than suitable for my usage.
16GB Vram can be eaten quickly with 3rd party detailed aircraft and heavy or not optimised scenery, so having 24 GB IMO is very recommended for MSFS.
Note I play at 4K.
Not having DLSS3 with the 3090 is not a major disadvantage for me, after trying it with the 4090.
The sim suffers more from low fps (20-25) when is limited by the CPU. DLSS 3 could double that but it’s still not ideal and it still does not feel smooth because native fps are low.
Basically, although DLSS 3 can help, it works best when there is less need for it.