Quote Originally Posted by The Verge
Asobo, the developer of Microsoft Flight Simulator, has been busy rewriting its engine to perform well on Xbox Series X / S, and the changes will also bring some much-needed improvements to the PC side on July 27th.

During a recent Twitch stream, spotted by Twinfinite, Asobo demonstrated just how significant the performance improvements will be on older systems with an Intel Core i7-9700K and an RTX 2060 Super. Microsoft Flight Simulator jumped from around 30fps to nearly a solid 60fps just thanks to the patch. CPU utilization also drops from 100 percent to 75 percent on this particular PC, and memory drops from around 16GB to 4.7GB.

While Microsoft Flight Simulator will move to DirectX 12 for Xbox Series X / S, the game will remain on DirectX 11 on PC for now. “All the performance improvements come from just improving the simulator,” confirms Wloch. “PC has not yet moved to DirectX 12, the team is still working on it. It may bring improvements further, or not.”
Microsoft Flight Simulator is getting huge PC performance improvements this month - The Verge
Update 5 vs Update 4 - MASSIVE Performance Improvement: