@raceman Just MSFS, FSX is even older than P3D, MSFS is the replacement for FSX. Anything 40th Anniversary would be MSFS. To try to clear up some acronyms, FSX is shorthand for Microsoft Flight Simulator X (X as in 10), came out around 2004 or so. MSFS is Microsoft Flight Simulator, also known as FS2020, because it was released in 2020. But I think most people just call it MSFS now. Hope that helps.
If you get Microsoft Flight Simulator, a lot of the 40th Anniversary stuff is free, either included with the sim, or a free add-on in the Marketplace. I don't know if any of it is payware, but I can't swear it's all free.