It’s been 5 mins and the Microsoft Store says “not currently available” and is it supposed to be on Game Pass on launch ?
It showed up on Gamepass for me, might just be that it takes a bit to propagate for all users. It should be available on the Xbox store, link is here: https://www.xbox.com/en-GB/games/store/train-sim-world-5-standard-edition/9N9FR8CSZP56/0010
Downloaded fine for me. Purchased the free version went into the store and selected the standard edition and then manage and it let me download the routes (Series X)