No, you need to purchase Destiny 2 on each platform you wish to play on. If you are referring to the pre-order bonus of being able to play Destiny 2 on your console when you order Shadowkeep, that is only applicable if you are buying Shadowkeep on the same console. On October 1st, all content from the first year of Destiny 2, along with some other features and content, will become available to all players for free. This is called Destiny 2 New Light. With New Light, you will be able to cross save your primary characters and play with them on any platform. If you play Shadowkeep on PC, you can still use what you've earned on your console, but you won't be able to participate in Shadowkeep activities unless you also buy Shadowkeep on your console.