Universal Package do support arbitrary metadata in the manifest file, and ProGet will display that on the UI. It's technically possible to add arbitrary metadata to other package files as well, although obviously ProGet could never know about or display that. However this metadata is not intended for searching or indexing.

ProGet does not support "arbitrary, server-side metadata" for any package types. In other words, you cannot simply "tag" or "annotate" otherwise packages after they've been added to ProGet.

This is intentional and by design, as it keeps the metadata contained to the manifest file (which is stored within the package file itself), which effectively makes it "cryptographically sealed" and cannot be tampered with.

So, as you migrate from Artifactory, you'll need to change your workflows to support a more modern, package mindset. In case you haven't seen it already, we have a Migrating from Artifactory to ProGet Guide that you may find helpful.

Best,
Alana