wifi weak security

The warning is telling you that your router is not using the current standard for security. You can change this by logging into your router and configuring the security.  Set it to WPA3 Personal for better security. Set it to WPA2/WPA3 Transitional for compatibility with older devices.

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. Whichever setting you choose, always set a strong password for joining the 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 (802.11ax), 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.
• WPA2 Personal (AES) is appropriate when you can't use one of the more secure modes. In that case, also choose AES as the encryption or cipher type, if available.

Recommended settings for Wi-Fi routers and access points - Apple Support

Check your WiFi Router / Modem for --> Recommended settings for Wi-Fi routers and access points ...

Consider more secure wifi configuration.

Change your router’s WiFi to use WPA2-AES (CCMP) with no WPA or TKIP. Updating this setting ensures that your devices always connect in one encryption mode

1. TKIP is obsolete and not considered secure. Choose WPA2, the latest encryption standard, with AES encryption for optimal security
2. If your router doesn’t specify TKIP or AES, the WPA2 option probably uses AES

See the pics below

In spite of Weak Security iPhone will connect to WiFi.