Answer: I would have suggested Cala Major as it’s physically the closest beach to the cruise port, but it’s not very big and it’s gets very busy with locals as well as holiday makers in August, so you may be better offjust going the extra 15 mins to Palma Nova, three wide beaches, lots of nice reasonably priced bars and restaurants along the front if you want something to eat during the day. Taxi from the cruise port would be around 20 euros. Few pics of the beach on the link below.
https://www.abc-mallorca.com/palmanova-beaches/