My bank wants such a contract!

When founding an entrepreneurial company in the so-called simplified procedure, the model protocol replaces the articles of association. This follows directly from the law:

§ 2 Form of the partnership agreement
(1a) … The model protocol is also valid as a list of shareholders. In other respects, the provisions of this Act on the articles of association shall apply mutatis mutandis to the standard record.

Thus, a partnership agreement is not permissible and not possible with this formation. If your bank or the tax office should require such “articles of association” or “shareholders’ agreement”, it is sufficient if you submit the sample protocol.