AMD 6800xt or 6900xt GPU. More VRAM,cheaper even brand new compared to Nvidia and better overhead in DX12.
I switched to AMD from Nvidia RTX a month ago and my experience with MSFS has been nothing but amazing despite the bugs in SU11. Rx6800 running most settings on Ultra 3440x1440. Fps varies. 70+fps in less intensive areas.
If you decide to switch to Nvidia you may find some good deals on the used market. eBay (Reddit r/hardwareswap)
Someone on hardwareswap sold their 3090 for 750USD.