Why am I seeing security warning on wifi

Those are two totally unrelated issues.

If the message is just Security Warning go to Settings/Wi-Fi and tap on the i next to your network name, tap on Private Wi-Fi address. If it says “Off” and this is your personal Wi-Fi network you don’t need to change it. But to make the message go away if it bothers you change it to Fixed. This feature prevents public Wi-Fi networks from tracking you through your Wi-Fi address, and it should be set to Rotating for all networks except your home (or work/school) Wi-Fi network.

Unfortunately, for the Facebook problem you will have to contact Facebook support.

There’s also the weak-security warning…

Here are the: Recommended settings for Wi-Fi routers and access points - Apple Support

If your Apple device shows a privacy warning or weak-security warning about a Wi-Fi network, that network could expose information about your device…