Opening the Camera app on iPhone is one of the most demanding tasks it can possibly do. Doing it and doing it fast means powering up the image sensor and its supporting hardware (ISP, ML hardware, etc.) and immediately terminating all non-essential tasks on the device so it can dedicate it to this.

If you don’t believe me, there are paths hardcoded in the kernel (I’m not joking: https://github.com/search?q=repo%3Aapple-oss-distributions%2...) to very quickly reclaim memory for Camera to launch.