At the Marriott Hotels brand, it's one $10 USD F&B credit per room
(not per guest) per stay
(not per day), if that's the Platinum Elite (and higher) Welcome Gift that the member chooses. Another Platinum Elite Welcome Gift option is 1,000 points. This is
in addition to breakfast for the member + 1 in the lounge (or in the restaurant if the lounge is closed or there is no lounge).
You should not have had to opt for breakfast instead of points. But it seems you actually opted for a $10 USD F&B credit instead of points. You would get breakfast for member + 1 regardless of your Platinum Elite Welcome Gift choice.
Perhaps you're thinking of Courtyard, AC Hotels, and Moxy, where the F&B credit is $10 USD
per day for
member + 1. However, at those brands, there is no other Platinum Elite breakfast benefit.
Look for table with the heading "ELITE WELCOME GIFT FOR PLATINUM ELITE MEMBERS AND ABOVE" at
https://www.marriott.com/loyalty/terms/default.mi