Series x

Not really...

Xbox Series X games / upgrades / updates has to be installed onto the Series X internal or expansion card SSD,

You can have Xbox One games on your external hard drive that will get an Series X upgrade but the games will need to be transferred to the Series X and then the Series X upgrade will need to be downloaded onto the Series X SSD,

As an example...

I have Marvel Avengers on my external hard drive that will get the Series X upgrade and I will transfer the game over to the Series X SSD ready to download and update the game to the Series X version when available.

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.

They released that game as a One version and as a Series S/X version. The Series S/X version will only work on a Series S/X.

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?

There's not a One X series. There is a One X and a Series X. A Series X (and Series S) are the newest consoles and what new games will be released for. Anything labelled as a One is old gen and studies are not releasing many games for those anymore.