The new sparking zero game said its optimized for Xbox series X and is not playable on this...

It says "Optimized for series X/S. IT should say "Only for series X/S. Why does Microsoft try to hide this with a little red circle popup note "not playable on this device" If it's not playable then keep it off my Game Pass ultimate and store

that I pay $16.99 monthly for.

Thanks. I know what you are meaning, but that's the list of the optimized games for this Series X/S gen. The Orange Box is a 360 game, optimized for Xbox One X (Xbox One X Enhanced), so backwards compatible, a game from previous generation (X360) playable on the Xone and also on the actual generation of console, thanks to the BC program of Microsoft. The game is not optimized for Series X/S, it would have to X/S logo like other games i own (Subnautica, We happy few etc). The only problem with this game is with the purchase from the Marketplace!

Because on my Xbox series x, it only shows 'Optimized for series x/s' but if a xbox series x version of a game is NOT 'optimized' how would i know if I'm playing a series x/s version of a game?

nope, most if not all current games on xbox one will be playable on the series x, eventually there will be games release just for the series x and they wont be playable on previouse console versions.

Xbox one s and Xbox one X are the same family, series x will be the new console and eventually (a couple of years down the line hopefully) games will only be release on the series x family so the xbox one x will not be able to play them.

If this is not confusing

No. Since it's only for the Series S/X it will not work on the One.