Unable to upgrade postgresql RDS version

Hello,

We are currently running our production rds on 10.23 version.. which is being deprecated.. So while we are trying to upgrade the snapshot it is npot being upgraded to the next version ie. 11*. We also tried modifying the version of postgresql versipn from 10.23 to 11.18 version ie. the latest major whcih was being provided.. so we tried that it took 3 hours for 200gib database but it was back to the older version ie. 10.23. So can you tell us what we can do regarding to the postgresql version upgrade, as most of our rds is running on the 10.23 version.