We run our own Docker registry on-prem with Harbor as well.

One issue to solve is auto-deletion of old images, so that the storage does not swell. Any tips?

https://goharbor.io/docs/2.13.0/working-with-projects/workin... seems like what you want, especially in combination with https://goharbor.io/docs/2.13.0/administration/garbage-colle...