Below are screenshots from the Toms Hardware test of the RTX 5090 Founders Edition.
MSFS 2020
MSFS 2024
Source Nvidia GeForce RTX 5090 Founders Edition review | Tom’s Hardware
I currently have an RTX 4090, a Ryzen 7 9800X3D and 64GB of RAM. I play at 2K resolution on an MSI OLED monitor with a 240Hz refresh rate. In Microsoft Flight Simulator, I use ultra settings at 2K resolution, Vsync - on, 33% refresh rate,TAA (DLSS and FG - off).
It seems that, in my case, upgrading from the RTX 4090 to the newer RTX 5090 won’t make much of a difference.
Therefore, I will most likely wait another 2-3 years for Nvidia next GPU series.