That is just totally false. Apple does not rely on security through obscurity. They may not publish the code for the SEP but they do have a whitepaper that lays out the key architectural features.[1]
The only reason your Linux laptop would be more secure than an iPhone is if you were using a high-entropy key to unlock it every time you wanted to use it -- and the iPhone wasn't. That's it. But remembering high entropy keys without storing them in some less secure manner is so inconvenient and failure-prone for most people that it's actually a less secure design than Apple's SEP-assisted approach. And you could opt-in to a high entropy key on an iPhone if you wanted to, so even that is a false comparison.
The only reason your Linux laptop would be more secure than an iPhone is if you were using a high-entropy key to unlock it every time you wanted to use it -- and the iPhone wasn't. That's it. But remembering high entropy keys without storing them in some less secure manner is so inconvenient and failure-prone for most people that it's actually a less secure design than Apple's SEP-assisted approach. And you could opt-in to a high entropy key on an iPhone if you wanted to, so even that is a false comparison.
[1] https://images.apple.com/business/docs/iOS_Security_Guide.pd...