two systems

As long as one is your home console and you are signed in on the other one on same account it will work .

But as said above it will show on any console you are signed into. 👍

If it is digital it should show up on either xbox so long as the profile it was originally downloaded to is on the xboxes your using if it is a disc of course you may have to install it.

It will show up on every console you are logged into.

You can only have 1 console set as your Home at a time. So if the Series X is set as the Home console, you will no longer be able to access the games on the One without the account that purchased the games.

Yes it is. However, be aware that the game is licensed to both the tag and 1st console that it was downloaded to. This means that anyone can play the game on the first console but no one will be able to play it unless you are signed in to the 2nd console
that it is downloaded to.