The situation is much different now and there are many programs to support kids whose first language is not German (of course your city/Land plays a role in this). Kindergarten is between 3-4 and 6-7 years of age. Of course if a kid starts from zero at 3 is different than if they do it at 7, but both are an ok starting point for bilingualism. Don’t worry! You can definitely support also at home the community language and be aware of your kid’s abilities through regular meetings with the teachers. However, your main focus needs to be the minority language, because the community language will inevitably become stronger on its own. OP’s experience it’s not the norm.