Hi @aharalambopoulos_3520 ,
ProGet works as a "Private Docker Registry" which seems to be different than a "Docker Hub Mirror".
Last time we researched Docker Hub Mirrors, they seemed to be primarily intended to provide image to certain geographic regions (like China) where Docker Hub content would otherwise be restricted. They could also be used to set up a "local mirror" of Docker Hub, but in all cases, it seemed to basically just redirect traffic from the default docker.io URL (or whatever) - so it wasn't intended to be used as "Private Docker Registries".
In any case, Mirrors don't seem to be a good fit for ProGet; instead, if you wish to use nginx, we would advise to "privatizing" and "lock" images using sematic tag, so that you can be assured that corp.local/images/nginx is a tested/safe image with tags you control.
Best,
Steve