If you own Xbox games digitally or have an active Xbox Game Pass Ultimate subscription, you can play those games on your PC without purchasing them separately. However, if you don't own the games, you will need to buy them or subscribe to Xbox Game Pass.
Because game progression in crossplay-enabled games is stored on your Activision account, you can play on any platform you have linked to your account, and your progression carries over. You can register for an account using an existing gaming account with PlayStation, Xbox, Steam, or Blizzard.