I hadn’t thought of it this way, but Apple’s new measures to battle child pornography and indecent photos sent to children is a kind of “back door” to encryption — a hole, access to which (as Apple famously and furiously argued) cannot be limited to the “good guys.”
UPDATE: Four days later, I’ve learned a bit more about this and my “back door” concerns are assuaged. Joanna Sterns Apple’s Child-Protection Features and the Question of Who Controls Our Smartphones is especially good, though it’s probably behind a paywall.