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.
Read the announcement for more information!
Features releasing from October 2019 through March 2020
Innovate, Collaborate, Grow - The top training and networking event across the globe for Microsoft Business Applications