If you have a 360 disc game and upload it to the cloud, can you not play it on the series s?

It's not possible to upload game data from a 360 disc to the cloud. The cloud on the 360 is for storing game saves, not the game itself. To play the game on the Series S, you would need to own the game digitally.

You have names mixed up. There are no consoles named the Xbox One Series S or Xbox One Series X.

The Xbox One/One S/One X all have a disc drive.

The Xbox One S All Digital Edition does not have a disc drive.

The Xbox Series X has a disc drive.

The Xbox Series S does not have a disc drive.

All the consoles can play backward compatible games. The Series S and One S all digital edition can only play games digitally downloaded.

The other consoles can play games from disc and from digitally downloaded,

I hope this clears things up for you.

Do you mean Series S or One S? If it has a disc drive it's a One S

Xbox One cannot play Flight Simulator except via the cloud using Game Pass Ultimate

If you are getting a "you need gamepass" logo on a Series, you need to reinstall the game to remove the GP tags

To add to what Gerardo said, when it comes to game saves for 360 games, the only way to transfer them over to an Xbox One/Series console is to upload them to the Xbox Network from a 360 console. If you've done that, when you launch a 360 game on your Xbox One/Series console that you have progress on, it will download a copy of the save from the cloud and you can continue on from where you left off. If you didn't upload your saves to the cloud, you'd have to start over from scratch unfortunately.

Since you have a Series S, you would need to purchase the game digitally in order to be able to play it. Since he has the game on disc, the disc needs to be in the disc drive in order to play it and that's not possible with a Series S.