You are using a development environment to add a new column to a system table.

Step 1: Create a new publisher

Solution publisher

Every app and other solution components such as entities you create or any customization you make is part of a solution. Because every solution has a publisher, you should create your own publisher rather than use the default. You specify the publisher when you create a solution.

Step 2: Create a new unmanaged solution and select the correct publisher

unmanaged solution

Unmanaged solutions are used in development environments while you make changes to your application. Unmanaged solutions can be exported either as unmanaged or managed. Exported unmanaged versions of your solutions should be checked into your source control system. Unmanaged solutions should be considered your source for Microsoft Power Platform assets. When an unmanaged solution is deleted, only the solution container of any customizations included in it is deleted. All the unmanaged customizations remain in effect and belong to the default solution.

Step 3: Add the table top the solution and add the new column.

Step 4: Run the solution checker on the solution

Use solution checker to validate your model-driven apps in Power Apps.