Google Cloud Artifact Registry supports multiple artifact formats, including a feature for Generic Repositories (currently available as a ‘Preview’ offering), which can store generic and immutable artifacts that do not need to follow any specific package format within Artifact Registry. You can store and manage arbitrary files such as archives, binaries, and media files without requiring package specifications.

You can explore this quickstart from the AR documentation, which might help you in trying to upload an AAR file to Artifact Registry. However, there is no guarantee of success, as the feature is still in Preview (limited support) and ongoing improvements are being made.

If you were unable to do it successfully, I suggest filing a feature request so Google's product engineering team can consider your preferred use case. However, please keep in mind that there is no ETA for a response or any guarantee that it will be implemented.