The EU VAT Assistant reached its end of life in June 2022 and we can no longer provide support for it, nor guarantee updates. We are keeping the plugin available for users who still use it, and might need to access its code, but we would recommend to contact your developers if you need assistance tweaking or troubleshooting it.
Due to this, there are no plans to further update the plugin to support the HPOS storage. Other developers who wish to contribute to that feature are welcome to do so.