In Google Cloud IAM: if a policy applied at the project level gives you Owner...

Policies are a union of those applied to resources themselves and those inherited from higher levels in the hierarchy. If a parent policy is less restrictive, it overrides a more restrictive policy applied to the resource. If a parent policy is more restrictive, it does not override a less restrictive policy applied to the resource. Therefore, access granted at a higher level in the hierarchy cannot be taken away by policies applied at a lower level in the hierarchy.