According to Apple, the security setting defines the type of authentication and encryption used by your router, and the level of privacy protection for data transmitted over its network. WPA3 Personal is the newest, most secure protocol currently available for Wi-Fi devices. It works with all devices that support Wi-Fi 6 (802.11 ax), and some older devices. WPA2/WPA3 Transitional is a mixed mode that uses WPA3 Personal with devices that support that protocol, while allowing older devices to use WPA2 Personal (AES) instead. This mode offers better security and compatibility than WPA2 Personal (AES) alone, and avoids the weak security and performance of WEP and WPA/WPA2 modes. References: Recommended settings for Wi-Fi routers and access points - Apple Support