which version of xbox series x have the best graphics?

Microsoft introduces "Smart Delivery" with the Xbox Series X, which means, that if you own an existing game (like Minecraft in your example, or Gears 5) or a new game comes out for Xbox One and Xbox Series X with improved graphics on Series X, you won't
have to buy the game twice.

With Smart Delivery you will play the "enhanced" version on Series X, and the "normal" version on Xbox One.

For more info about Smart Delivery and other terms used with the Series X check this page: https://news.xbox.com/en-us/2020/03/16/xbox-series-x-glossary/

As with the Xbox One X, games that are Enhanced for this specific console will be rendered in 4K, and then downscaled to 1080p, which will result in much smoother and better looking graphics than "directly" rendered 1080p.

So with the Series X you would get the best 1080p graphics.

Well no as smart delivery gives you the best version for your console only advantage is the better graphics series x or compressed files if you are using series s

If you didn't want the previousngen you shouldn't.have bought the cross gen version

It's very easy how to check which version of the game you bought. Check the game case. If it says, Xbox One & Xbox Series X|S, then you have the Xbox One version of the game. If it just says Xbox Series X|S, then you have the Xbox Series X|S version.

I would presume that if a game is Xbox One X Enhanced, those benefits will also appear when the game is played on Xbox Series X, along with any Optimized for Xbox Series X benefits that same game might receive through future updates. I doubt seriously it
would be a step backward when played on the superior hardware.

Keep in mind the Smart Delivery feature, which will enable Xbox Live to send the best possible version of the game to Xbox Series X automatically. So that may be the Xbox One X Enhanced version, or (if the developer makes such an update possible) the Optimized
for Xbox Series X version. Given the choice, I'd want the Optimized version.