hey my iPhone 12 mini won't connect to wifi and the cellular data says error. How do I fix this?

Try first to optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

Thwn see the following Apple articles:

Connect to Wi-Fi on your iPhone, iPad, or iPod touch

Connect to Wi-Fi on your iPhone, iPad, or iPod touch - Apple Support

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

If your iPhone, iPad, or iPod touch won't connect to a Wi-Fi network - Apple Support

Within the last five days or so, I am suddenly unable to connect to Wifi. Even at home I can't. Wifi is with Xfinity, I have the name and password to the WiFi, however, it won't open on my phone. I need to get Wifi up and running. Please let me know how I can fix it.