I found this on forbes:
The Xbox Series S will output at 1440p rather than 4K, but it will still upscale on 4K television sets. The framerate will be the same on both machines and while the Series X might look a little bit better, the Series S will still have great-looking games and a fraction of the cost.
You’d think less RAM and a smaller SSD would hit the Xbox Series S’s performance, but it really shouldn’t in practical terms. Games will require less memory and storage space since they’ll be playing at 1440p and using smaller assets. This allows developers to decrease file size for Xbox Series S games, taking up less space on your SSD.
So long as you’re fine with 1440p, the actual difference here should be fairly negligible. It’s possible that having less RAM will impact performance, but the hit won’t be too big, and if you don’t have a 4k TV it shouldn’t matter at all. Meanwhile, the Xbox Series S will upscale to 4k.