As far as shopping portals, I believe JetBlue is the only one to offer points for shopping at
Amazon. Marriott’s MORE app briefly offered points for shopping at Amazon, but Amazon was taken down as a merchant within the first few days and there’s no word when or if it’ll return.
Another way to earn miles and points on Amazon purchases is to use your choice of credit card to buy Amazon gift cards that you can load to your Amazon gift card wallet. The MileagePlus X (MPX) app earns you 0.5 MileagePlus miles per $1 spent on Amazon egift cards, plus a 25% mileage bonus if you have a MileagePlus credit card added to your MPX account (you don’t have to put the actual purchase on it), plus whatever miles or points you’d earn on the credit card you use to pay. The Gyft app sells Amazon egift cards, which I believe still earns 3x Ultimate Rewards points per $1 using Chase Ink Preferred and 5x UR when using Ink Cash or Plus through PayPal checkout. The Swytch app also sells Amazon egift cards, and I believe codes similarly to Gyft when using Ink cards and paying through PayPal. Then you can also buy physical Amazon gift cards from grocery stores using a credit card with a high bonus grocery category like the Amex Blue Cash Preferred (6% cash back), or from office supplies stores with the Ink Plus or Cash (5x UR).
ETA: I stack earning rewards from buying Amazon gift cards with a credit card and MPX with the JetBlue rewards for shopping through their partners portal.