Is the landlord obligated to renew the lease at the end in perpetuity? Or does the landlord just need to wait for the lease to expire and then choose to not renew?

in germany by law every lease for private homes is always in perpetuity. the concept of renewal does not even exist. it is always month to month until the tenant decides to move out. you can't not renew a lease. you can raise the rent, but only in small steps. exceptions are if the tenant fails to pay for a few months, damages the property or misbehaves in other ways.