Obscurity is a delay tactic which raises the time cost associated with an attack. It is true that obscurity is not a security feature, but it is also true that increasing the time cost associated with attacking you is a form of deterrant from attempts. If you are not at the same time also secure in the conventional sense then it is only buying you time until someone puts in the effort to figure out what you are doing and own you. And you better have a plan for when that time comes. But everyone needs time, because bugs happen, and you need that time to fix them before they are exploited.

The difference between obscurity and a secret (password, key, etc) is the difference between less then a year to figure it out and a year or more to figure it out.

There is a surprising amount of software out there with obscurity preventing some kind of "abuse" and in my experience these features are not that strong, but it takes someone like me hours to reverse engineer these things, and in many cases I am the first person to do that after years of nobody else bothering.

This is a tired trope. Depending exclusively on obfuscation (security by obscurity) is not safe. Maintaining confidentiality of things that could aid in attacks is absolutely a defensive layer and improves your overall security stance.

I love the Rob Joyce quote that explained why TAO was so successful: "In many cases we know networks better than the people who designed and run them."

I think you are conflating:

Is an unbreakable security mechanism

with

Improves security

anything that complicates an attacker improves security, at least grossly. That said, then there might be counter effects that make it a net loss or net neutral.