Turns out setting keycloak.persistence.deployPostgres is necessary because keycloak itself has a condition on the postgresql dependency, and apparently values used for dependency conditions in requirements.yaml don't pass through subcharts (so infrastructure.activiti-keycloak.keycloak.keycloak.persistence.deployPostgres is not the same as keycloak.persistence.deployPostgres).
Enabling Keycloak persistence should be added to the documentation. The following was tested on AWS EKS for Activiti Cloud 7.0.0 SR1
Turns out setting keycloak.persistence.deployPostgres is necessary because keycloak itself has a condition on the postgresql dependency, and apparently values used for dependency conditions in requirements.yaml don't pass through subcharts (so infrastructure.activiti-keycloak.keycloak.keycloak.persistence.deployPostgres is not the same as keycloak.persistence.deployPostgres).