I can only suggest that you read the link that I put on the post for Princess USA.
It clearly says that. 'Up to Date' is "Received all recommended COVID-19 vaccines, including any booster dose(s) when eligible at least 7 days before embarkation"
You are therefore up to date if you have had the original two shots plus any other booster that you have actually been offered and had at least 7 days before you depart.
If you have not been offered a first or second booster then as wowzz says above this does not mean any boosters that are upcoming in the future, so you are up to date. If you have been offered one booster and have had it you are up to date. If you have been offered the over 75 booster and have had it you are up to date.
I am cruising ex Southampton next month, I have only had one booster and I am up to date because no other jab has been offered to me.