Can I transfer a game purchase from one platform to another?

Short answer: unfortunately, you can't.

Jackbox Games does not control the various stores and marketplaces where our games are sold, and as a result, you can’t transfer purchases between platforms. In order to have the game on a new platform, you must purchase the game on that platform. This includes transferring activated game purchases from one Steam account to another. Do note that because those game purchases are linked to your Steam account, you will have access to them from any compatible device where you are logged in to that same account. So if you've just gotten a new computer, for example, that is not considered a transfer of your purchase across platforms and they will still be accessible.

Additionally, there is an exception to this rule:

• The Jackbox Party Pack 7 is the first title we have been able to offer as a universal purchase on the Mac App Store. This means a single purchase (from the Mac App Store) gives one access to the game across MacOS computers, iPad devices, and Apple TVs.
  
  Only Party Packs 7, 8, 9, 10, the Party Starter, and the Naughty Pack are available in this way; for all games prior to Pack 7, the Mac OS version requires a separate purchase from the Mac App Store.
  
  
• When purchasing older titles from the Mac App Store, the Apple TV (tvOS) version of our games can also be played on iPads (iOS), and vice versa. This includes The Jackbox Party Pack 1, 2, 3, 4, 5, 6. More current titles are universal purchases as above.