The Secure Enclave is a security chip in the iPhone that prevents software from being able to access secure information like encryption keys. Apple uses random encryption keys unique to your iPhone that are protected by the Secure Enclave chipset. All iPhone devices after the 5S feature a Secure Enclave chip to dramatically increase the security of the device. These chips are present in most Apple devices and makes iPhone devices significantly more secure than other options if someone gains physical access to your device.
According to the Chinese hackers Pangu Team, there is currently an "unpatchable" exploit for the Secure Enclave chipset. "Unpatchable" means it cannot be fixed via software updates and would require hardware modifications. The A12 and A13 Bionic chips do not seem to be effected by this vulnerability.
As of right now, Apple has not released any comments that I can see. They are likely discussing the exploit with Team Pangu prior to making an official announcement.
As of right now, the only way to protect yourself from this attack is to have an iPhone 11 or higher. If someone gets physical access to your device (like Border Patrol), they can potentially gain full access to the device and potentially anything encrypted on it.