Why some games still require me to buy even I already have gamepass ultimate?

Thank you and I apologize but seems like the games were no longer part of the Xbox Game Pass library which is why you're being asked to purchase the games.

For your reference, you can check this link: https://www.xbox.com/en-US/xbox-game-pass/games

Hi, I hope you're doing great out there. I am an Independent advisor and I am here to help you in regard to your concern.

We need to validate if these games are still on the game pass library.

May I ask what are these games?

Hi Francis, I was looking for Lego Indiana Jones & Rayman from Xbox 360 games.

Some of the games on PC are availble on gamepass on Xbox however not all of them such as Age of empires as it requires a mouse and keyboard. Also gamepass for PC is a separate subscription to Gampeass, you would either have to buy another gamepass subscription
or get Gamepass Ultimate which works both on PC and Xbox

Yes you keep all of them. *Outside of games with gold*

On a side note Gamepass games however require you to have active gamepass to play them *Unless you already owned/bought them*

I would like to add that even if you own a Gamepass subscription you need to have Xbox live gold to access online features within the games on the Gamepass program