You can use Revolut for that. Top up your Revolut account with your M&M card, then transfer the money into your US bank account. It is sent as a direct deposit.
Revolut offers the mid-market exchange rate (=no FX fee) and you’d top up your Revolut account in EUR.

Also, I think that apart from the 5x on flights, the US Platinum card generally isn’t worth it anymore. Even US residents are canceling it in droves. I’d look into cards with a lower annual fee/better value proposition. Amex Green/Gold, Chase Sapphire, Citi Premier, etc.