Are you asking in terms of between you and Micrsoft or between you and your employer?
If you are concerned about MS then I would assume you own any intellectual Property produced. Although I don't see how you would use it outside of PowerApps, which MS owns.
If you are concerned about your employer/client that would be dependent on how your employment agreement is worded.
Unless the partner developed it in a contract with MS then the partner should retain the IP rights. But as I said, they won't be worth much without PowerApps, which MS owns.
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