As a white male developer, what can I do to support Black Lives Matter?

Reach out to other white males.

It doesn’t need to be awkward, complicated, or in depth. Whenever a colleague flirts with casual racism, saying “let’s keep things professional” works wonders.

Beyond that it depends on your position and abilities.

Publically tell police and politicians that they do and if they don't agree you will vote for leaders that will.