Affinity Federal Credit Union has a credit card with 5% back on Amazon and bookstores. Sometimes they have promos (possibly targeted). For example right now I have one that’s giving an extra 1% back on $2000 over a 2 1/2 month period, which pushes that up to 6% cash back.

An important thing here IMO would be to factor in both standard best card rankings (ex. 3% back on online shopping) AND specific card offers (ex. Get $15 back if you spend $30). I think there's no good way in the app today, that I'm aware of at least, that combines both of these side by side to truly tell me which card to use.

I would love to be able to do this with online grocery stores for my CSP.

This will be great. At this moment my discover card is offering from OCT-DEC a 5% cash back on amazon.com , target.com and walmart.com . That is not showing up on the app suggestions

It already exists under Category - Online Shopping