It seems something might be wrong with the logic for the new defaultChannel property. After initially syncing an operator to a tarball, subsequent runs complain the catalog is invalid, as if defaultChannel was never set.

I tried oc-mirror v4.14.16 and v4.15.2

100%

kind: ImageSetConfiguration
apiVersion: mirror.openshift.io/v1alpha2
storageConfig:
  local:
    path: ./operator-images
mirror:
  operators:
    - catalog: registry.redhat.io/redhat/redhat-operator-index:v4.14
      packages:
        - name: openshift-pipelines-operator-rh
          defaultChannel: pipelines-1.11
          channels:
            - name: pipelines-1.11
              minVersion: 1.11.3
              maxVersion: 1.11.3

oc-mirror -c ./isc.yaml file://operator-images

$ oc-mirror -c ./isc.yaml file://operator-images
Creating directory: operator-images/oc-mirror-workspace/src/publish
Creating directory: operator-images/oc-mirror-workspace/src/v2
Creating directory: operator-images/oc-mirror-workspace/src/charts
Creating directory: operator-images/oc-mirror-workspace/src/release-signatures
No metadata detected, creating new workspace
wrote mirroring manifests to operator-images/oc-mirror-workspace/operators.1711523827/manifests-redhat-operator-indexTo upload local images to a registry, run:        oc adm catalog mirror file://redhat/redhat-operator-index:v4.14 REGISTRY/REPOSITORY
<dir>
  openshift-pipelines/pipelines-chains-controller-rhel8
    blobs:
      registry.redhat.io/openshift-pipelines/pipelines-chains-controller-rhel8 sha256:b06cce9e748bd5e1687a8d2fb11e5e01dd8b901eeeaa1bece327305ccbd62907 11.51KiB
      registry.redhat.io/openshift-pipelines/pipelines-chains-controller-rhel8 sha256:e5897b8264878f1f63f6eceed870b939ff39993b05240ce8292f489e68c9bd19 11.52KiB
...
  stats: shared=12 unique=274 size=24.71GiB ratio=0.98
info: Mirroring completed in 9m45.86s (45.28MB/s)
Creating archive operator-images/mirror_seq1_000000.tar


$ oc-mirror -c ./isc.yaml file://operator-images
Found: operator-images/oc-mirror-workspace/src/publish
Found: operator-images/oc-mirror-workspace/src/v2
Found: operator-images/oc-mirror-workspace/src/charts
Found: operator-images/oc-mirror-workspace/src/release-signatures
The current default channel was not valid, so an attempt was made to automatically assign a new default channel, which has failed.
The failure occurred because none of the remaining channels contain an "olm.channel" priority property, so it was not possible to establish a channel to use as the default channel.

This can be resolved by one of the following changes:
1) assign an "olm.channel" property on the appropriate channels to establish a channel priority
2) modify the default channel manually in the catalog
3) by changing the ImageSetConfiguration to filter channels or packages in such a way that it will include a package version that exists in the current default channel

The rendered catalog is invalid.

Run "oc-mirror list operators --catalog CATALOG-NAME --package PACKAGE-NAME" for more information.

error: error generating diff: the current default channel "latest" for package "openshift-pipelines-operator-rh" could not be determined... ensure that your ImageSetConfiguration filtering criteria results in a package version that exists in the current default channel or use the 'defaultChannel' field

It should NOT throw that error and instead should either update (if you've added more to the imagesetconfig) or gracefully print the "No new images" message.