It looks like the Postfix default database type changed from lmdb to hash in the new V4.0.1 release. Whe´re using the HELM chart to deploy to K8s.

Whe´re using a transport_maps entry transport_maps: "lmdb:/etc/postfix/recipient_dependent_relayhost" which is not working any more in the new release.
When i add postfix.default_database_type: "lmdb" to the values.yaml it works as before.

There is also a Warning in the logs which i did not spot in older releases:
warning: inet_protocols: disabling IPv6 name/address support: Address family not supported by protocol