Internships are a brilliant way to gain knowledge. Why not check out Leipzig which at the current time has 2 internship vacancies where you can learn Product Development skills. Business Development and Computer Science are at the current time the most sought after subcategories for this area. Vacancies that involve Software Development, Product Management, and New Product Development are at the current time quite common on Jobspotting.
If you're eager to work for a startup, it is a good idea to try similar sectors or other nearby cities. As it stands, there are no startups seeking Product Development expert knowledge. Use the Explore search bar to learn about jobs in other areas of expertise or locations.