It was, indeed, on the brake pedal. “Firm” pressure was, indeed, being applied, and the parking brake was set with enough force to prevent movement.

Without the engine running, there is no vacuum boost on the brakes. “Firm” pressure on the brake pedal is not sufficient to overcome the high torque of a starter motor against first gear, even with an adequately set parking brake as well. If you’re going to insist on having the transmission in gear, the highest gear would be the best alternative to neutral, as it provides the lowest torque fighting the brakes.

The amount of pressure on the brake pedal needed to stop the vehicle without boosted brakes would better be described as “standing on them like your life depended on it”, but you only asked for “firm”. The measure you have put in place to mitigate the observed danger is demonstrably inadequate, and you have yet to offer any sort of reasoning for your “first gear” suggestion.

But, this is all a digression. Your position is that the vehicle should be in first gear. The only explanation you have offered for that is the possibility of failing a German driving test. “Preventing Injury or property damage” is a far higher priority than “appeasing some authoritarian twat”, so I’m going to need a better explanation from you for first gear.