It says the game is not available for my platform

That means no build of this game exists for the operating system you are running the launcher on — the developer has not published one, or has not published one yet.

It is not a fault with your account, and it is not something support can switch on. If you own the game on another platform, it stays yours there. Games list the platforms they support on their store page, so it is worth checking that before buying on a new machine.