Migrate RDS in us-east-1a

I'm trying to migrate a PostgresQL 10 RDS DB to version 14. No matter which instance type I try, it says that it's not available in our availability zone (us-east-1a). Types we've tried:

db.r6g.large db.r6i.large db.r5.large db.t4g.xlarge db.t3.xlarge db.r5b.large db.m6g.xlarge db.x2g.large db.m6i.xlarge

What can we do?

Best Regards, Ortwin