According to this guide, the Apple Card’s sleek titanium body is allergic to two of the most common materials within which credit cards can be found: leather and denim. Apparently these materials “might cause permanent discoloration that will not wash off.” So, if you like to keep your leather wallet in the pocket of your jeans, this is not the credit card for you. The card should also not be kept too close to loose change, keys, other credit cards or any other objects that you might have in your purse or pocket, lest they scratch it.
If despite all of these efforts the card still somehow manages to get dirty, it can only be cleaned with a damp, lint-free microfiber cloth followed by another microfiber cloth “moisten[ed]” with isopropyl alcohol. Any other type of cleaning cloth or solution is likely to damage it.