The clear winner for MSFS (and any gaming workload right now) is the Ryzen 5 5600X, better single and multi thread performance than the Intel chips. Just in short supply.
If you want more cores/threads, you can go with a 5800X, but anything over that is a complete waste, since those cores/threads will simply not be utilized.
Some additional info:
Ryzen 5 5600X vs. Ryzen 7 5800X vs. Ryzen 9 5900X & 5950X: GPU Scaling Benchmark - YouTube