When you upgrade pgsql, it always keep the older version until you migrate it manually.
I’m not very familiar with psql, so I don’t know the exact command to execute. But I think it would be something like:
# Stop postgresql
systemctl stop postgresql
# Drop the new cluster. WARNING: only if it is empty. If you have another application that is using it... Don't. In such case, I don't know how to do, check the manual
pg_dropcluster --stop 14 main
# Then migrate data from old cluster
pg_upgradecluster -m upgrade 11 main
# Start and test
systemctl start postgresql
Please note that i’m not sure of these command, you should check for an online tutorial to confirm.
If everything works, you should also drop the data from the old cluster (I don’t know the exact commands)