Do you have to already own a Apple product to apply for the Apple Card

You’ll need to acquire an iPad or iPhone.

From the How your Apple Card application is evaluated - Apple Support article, you’ll need to have an iPad or iPhone:

From the fine print of another article:

To access and use all Apple Card features, you need to add Apple Card to an eligible iPhone or iPad that you own with the latest version of iOS or iPadOS. Then, you can manage your Apple Card on your device and make purchases anywhere Mastercard is accepted. If you don't add Apple Card to an iPhone or iPad that you own, you can only use your Apple Line of Credit for eligible purchases online and in-store at Apple.

There's a page of info on the Apple Card here.

https://support.apple.com/en-au/HT209257

Hope it answers your question

Cheers!