Amateur races - you need a license (e.g. join a club (“Verein”).
Jedermann races - these are often Gran Fondos (“Radmarathons”). License-holders and non-license holders can start. However, only Cat C Amateurs/license holders can start. Cat A and B not. These races do not have to follow the National Cycling Federation’s (BDR) rules. Organizers can do what they want.
Hobby races - “normal” road races and crits. Only non-license holders. Races have to meet the National Cycling Fed’s requirements.
From a participant’s perspective Jedermann and Hobby is the same. Race characters are often different. I don’t know how good your German is but here you’ll find a proper definition: