Oh! That is an angle I didn’t consider. I’ll start looking into possible signals I can send. Thanks!

In my opinion bicycles should not have a high beam

This is StVZO-compliant light, i.e. has a sharp beam cutoff.

Look inside, do any components look fried?

Tracing the circuit was my first thought. It would be difficult to open the housing non-destructively. Even if I could open the housing, getting it back together and restoring its IP rating would be sloppy at best.

Can you get the led to light by applying the a low voltage with a current limiting resistor directly to it?

Yes, the low beam works starting at ~7V with the negative and positive supply attached as pictured.