I couldn't find anything in T&C that said purchasing the GC with a Platinum Amex would not earn 5 points / $ in addition to the 4 miles / $. I think the GC just has to be for $250 or more to get the 4 miles / $.

This article is from 2019, but it states that certain Amex Cards do not earn points for gift card purchases. Supposedly the Amex Platinum should work. Others like the Amex Gold do not. I figured I'd go for it and bought some with my Platinum.

https://thepointsguy.com/credit-card...ard-purchases/

"The good news is that this change doesn't appear to be affecting all Amex cards. In addition to the American Express® Gold Card, it has affected the Blue Business®️ Plus Credit Card From American Express and the Blue Cash Everyday® Card from American Express, which are both showing gift card exclusions for everyday spending. But The Platinum Card® from American Express, the Amex EveryDay® Credit Card and the Marriott Bonvoy Brilliant™ American Express® Card are not"