Cannot play Apps on XBOX that were installed by another account

only if the achievements were made on your account, if they were done on another account those achievements are now that person's (as achievements are locked to the account that is playing the game on that console) and they cannot be transferred to your
account.

As long as you're on the same account that purchased the games, they should show in your library in the Xbox app or give the option to install when you look them up in the store. If they don't, then they were either bought on another account or if you previously played them through Game Pass, but no longer have Game Pass it would do that too.

Any games that are backwards compatible should show as ready to install in your Games and Apps as long as you're signed into the account that purchased the games. Is it possible they were purchased on another account?

Hi there,

if you were using the same account on the PC as you are on the Xbox One console, then the game should be available for you to install in the Ready to Install (My library) section on the console in My Games and Apps.

If you used a different account, then you will have to add that account to the console so you can install it on the console.

See this link for some more info:
https://beta.support.xbox.com/help/games-apps/game-setup-and-play/install-games

Then you were likely doing it on another platform, you cannot install external mods on Microsoft store games