I have both a Series X and two Series S consoles and bounce between them frequently depending on where I am. The Series S is a completely capable machine and I love it. If playing on a 4k screen, the Series S may have a decreased resolution (depending on how the developer made the game) as opposed to the Series X output, but it really isn’t a big deal for me. For example, playing Insurgency Sandstorm is sharper on my Series X, but the same game’s decreased resolution on my Series S doesn’t affect my gameplay at all. But if you are on 1080p displays, you may not notice much of a difference at all! I would totally buy the Series S. It’s just such a fantastic deal and such a cheap way to get into GamePass games. I bought one of my Series S consoles on Facebook Marketplace for $100. That’s an insane deal.
You will notice a decrease in performance on the Series S. It really just depends on how much you are willing to spend. It’s hard to say how much of a difference there will be because every game and developer is different. I play MSFS on the Series X but have not tried it on my Series S yet. I would expect a decreased resolution on the Series S or some other measure of decreased performance. Maybe less anti-aliasing? However, the Series S is an unbeatable Gamepass machine for super cheap. As I mentioned below, I got my second Series S for $100 on Facebook Marketplace. Have a look at some YouTube videos that discuss this very topic. Here is a direct graphics comparison for MSFS!