Business Central connector for Power Automate as well as Dataverse Virtual Tables are based on standard or custom APIs.

Fields that are exposed through those APIs are predefined - and there's no way to customize them. If a given field is missing the only workaround is for the partner do define a custom API page that includes all needed fields:

https://learn.microsoft.com/en-us/dynamics365/business-central/dev-itpro/developer/devenv-develop-custom-api

Currently partners need to create custom API pages ... or use some of the commercial tools to generate API objects.