Weak WiFi security! What to do…

You will need to reset security settings of your router. You can find instructions in the manual or online by searching for your router's make and model. If the router is provided by your service provider, you need to contact them. These are Apple's recommendations for the latest security settings...

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

Change the settings on your router to WPA2 AES or WPA3. Exactly how you do that depends on the brand and model of your router. If you don't have instructions for your router, do an internet search for instructions for your router's brand and model.