I was facing the same problem. Fixed it by going to the file on XCode - Pods > Pods > RCT-Folly > Time and comment the line "typedef uint8_t clockid_t;" and changed the "__IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_10_0)" to "__IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_12_0)".