Can International Student become a co-founder for startup business?

I am a foreign PhD student on a student visa in Berlin and am from Non-EU States. I have experience in quality management and a very good friend (German citizens) wants to leverage on my experience, to be a co-founder of a startup business in Berlin. I wish to know if I can hold passive investments in a company (as a co-founder). Can I form a business with a German, own shares in the startup business, and probably be functioning in a management role, rather than running the business?

I would appreciated answers to my question and further advice on what to do. I know you’re very busy so I appreciate any time you can give to respond to my query. Thanks very much.​​​​​​​