wifi security

This is NOT an iPhone problem; it is a problem with your router settings.

A "Weak Security" notification means that your Wi-Fi router is not configured correctly. There is a new feature in iOS 14 that checks and displays a message if your router is not using the most up-to-date security settings. Note that your router has always had weak security, you just didn’t know about it until now. 

See this Apple support article for how to configure it correctly—>Recommended settings for Wi-Fi routers and access points - Apple Support, specifically the section headed Security. And don't forget to configure your range extenders (if any) also!

After you change the router settings you should Forget the network in your phone settings and reconnect.

Note also that weak security does not interfere with using Wi-Fi, it is just a warning. Your Wi-Fi should still work normally, and, if it doesn’t, it is not because of the weak security message.

While the Wi-Fi network connection is fine, the Wi-Fi security configuration is weak.

You can continue to use what you have here, though you will see diagnostics related to security.

Your Wi-Fi router is running WEP, WPA, or WPA2 TKIP security and which is weak, and is not running WPA2 AES, WPA2/WPA3 transitional, or WPA3 security, and which is not weak.

Usual path is to ignore this, or to reconfigure your Wi-Fi router security(if your router can be reconfigured for this), or acquire a newer Wi-Fi router. If you’re renting your Wi-Fi from your Internet service provider and have an old router, a replacement Wi-Fi router from your ISP is a common solution.

If you want to discuss this further here, please post he manufacturer and specific model of Wi-Fi device, and whether you have credentials to access it.

You need to change the security protocol on your router.

Google your make and model to find out the steps.