No Options to migrate from RDS Postgres to Aurora

I'm trying ensure migrating from Postgres to Aurora works on my account using methods 1. snapshots and 2. read replicas here: https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraPostgreSQL.Migrating.html

I have tried various versions of postgres from 10.x, 11.x, 13.4 but

1. "Migrate Snapshot" option is greyed out under snapshot > actions
2. "create aurora replica" not showing under actions

I don't believe there is an issue with my account because I can "Migrate Snapshot" of other public postgres snapshots fine. it's just my own instances I cannot migrate from.