Can I play an Xbox Series X game on an Xbox Series S?

Xbox One games can be played on the Series S/X, but Series S/X games cannot be played on the One.

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?

It's important to know which game your friend bought.

I say this because there are currently three versions of the Series X/S game. Gta 5 Online, Gta 5 Series X/S and Grand Theft Auto V (Xbox One and Xbox Series X|S).

If he has purchased Grand Theft Auto V (Xbox One and Xbox Series X|S), which gives access to the game for Xbox One and Xbox Series S/X, he can play online with you as long as he downloads the Xbox One version, so you and he will have the same save and can play online.

If he is a Game Pass Ultimate subscriber he can download the game in the Xbox One version and play with you.

I have the Xbox one X project Scorpio, I was told that the game can be downloaded in any serie X or serie S (included mine), thanks for the help!!

Game can only be downloaded on a Series S and Series X, but not an Xbox One X. Xbox One X is not the same as a Series X.

I just bought a brand new Xbox One X, but when I go to the store, Flight Simulator and other Xbox Series X/S games say they are "not playable on this device" and I can't get Flight Simulator to install on my brand new Xbox One X because it says it's "not compatible". Very frustrating.

So you bought an Xbox One X and expected to be able to play an Xbox Series X game on it?

Why would a game made for an Xbox Series X work on an Xbox One X?

If you want to play Xbox Series X/S games I would take your brand new Xbox One X back to the store you bought it and see if they will take it back and you could try and buy an Xbox Series S (Series X consoles are very hard to find, but a Series S can be found fairly easilly)