No UI out of the box (Registry:v2). DTR has a 'health' UI that is pretty worthless since you can't browse images. There are other frontend tools that work with registry:v2 though, such as Portus:

https://github.com/SUSE/Portus

It's also, in my experience, much slower (inexplicably, since apparently Docker Hub is also backed by S3 under the hood). Using the official docker registry images (only modification was to point them to a private S3 bucket w/ credentials) resulted in frequent push/pull failures with 500 errors. Even when they succeeded, images were taking ~15-20 minutes to push. I filed a GitHub issue and the only suggestion was to decrease the chunk size, which did not improve anything.

Now we use quay.io and it's much easier and faster.

What would you actually want to use the UI for? For my part, all interactions with the registry are entirely automated. We set it up, and I forgot all about it. It's low level plumbing.