As-salamu alaykum. In Germany, legal health insurance is mandatory. My insurance offers a yearly budget/bonus program where they give me cash back (e.g., for registering a birth or the partner's birth preparation course) if I submit the receipts. Is it halal to accept and use this money?

Ustadh AbdulAziz al-Haqqan

Since the insurance is compulsory, there is no sin on you for being in it, and you may take back up to what has been paid in for you, so this bonus is fine as long as your total does not exceed that. Whatever is beyond it is not yours.