Why are games available in store but you can't play them?

Those games were delisted due to licensing issues. They're still listed in the store for informational purposes and people who bought the games before they were delisted, can still reinstall them.

These advisors need to read up on how optimized games play or don't play on a SeriesX/S.

Games that are optimized for the SeriesX/S CANNOT be played from an external HDD and that'll be why you can't load those game.

With the games telling you that an upgrade is available that'll be why you can't load them unless you install them on the internal storage.

Ok now I know why I can't buy it without a credit card on the us store. But why is the game not available at the German store?

There's 2 versions of the game available on the store for digital purchase.

Can't link it for you at the moment as the store is playing up.

Can't understand why cross chat wasn't available seems daft that even if you can't play games together