My Xbox series X also says is just an Xbox one and won't allow me to install some games...

I own the game on the Xbox series x but it won't allow me to connect the game to my profile which is on the Xbox series x and so it does not let me play online, If that makes sense.

Just to point out, I see some people making the mistake of referring to the new Xbox Series X. This question is specifically for the Xbox One X, not the new console. I have no intention of buying the new Xbox Series X.

The same thing applies to the one x. There are even some developers that have came out and down right said they would never allow their games to be backwards compatible. So no not everything will be. They have also stopped working on backwards compatibility
for the xbox one as that team is working on the series x right now.

Since I got a series X. My borderlands 3 game would not appear in my series X ready to install section. I have it on my Xbox one but it just doesn't appear on the series X for some reason. It's all under the same account as well

My Xbox series x 2k24 game won't install and says I have to buy the game for like 30 to 40$ when I have the disc

Same here.

I upgraded from the ultimate pass on Xbox one X to the series X but it won't let me claim it on the series X.

Also Tetris connected won't open either.