If you are using RDS Aurora PostgreSQL v10.12, v10.13, or v11.8, please be aware that they have been removed from the catalog and you can no longer create new clusters with these versions.

Error: error creating RDS cluster: InvalidParameterCombination:
Cannot find version 10.12 for aurora-postgresql
status code: 400

Bug Details: The problem relates to “NOT EXISTS” queries, insomuch as v10.12 ignores the “NOT” part, and gives you the exact opposite result. One workaround is to add “AND <column> is NOT NULL” to all affected queries.

Update 18/09/2020: All versions are back in all regions.