Is it possible to move every deployment on a running k8s cluster to another running k8s cluster? I don't need to move cluster configurations, just every deployment, its pods, secrets, services, endpoints, pv/pvc, ingress etc. Everything that would be attached to a namespace and deleted in case that namespace gets deleted.
As @Jonas suggested, except for PVs, you can apply the same Yaml manifests to migrate every deployment from one kubernetes cluster to another cluster. For PVs, you need to backup and restore PVs by referring to the official kubernetes doc on Creating volume snapshot and Restoring Volume from Snapshot Support.
Volume snapshots provide Kubernetes users with a standardized way to copy a volume's contents at a particular point in time without creating an entirely new volume. This functionality enables, for example, database administrators to backup databases before performing edit or delete modifications.
You can also use the Velero, pv-migrate tool/kubectl plugin and similar github issue for more details, which will help you to easily migrate the contents of one Kubernetes PVC to another.