iPhone 12 will not load without wifi

If you have an add-on first-few-hops VPN client app installed, remove that, restart the iPhone, and try again.

Though you’ve already tried a restart, a forced restart can sometimes clear odd problems:

… Force restart iPhone - Apple Support

I’d also check with your cellular carrier. The issue here could be specific to your plan, or to your carrier.

Hey there jawood9250,

From the details you provided, we're not quite sure what exactly is happening when only using cellular and not Wi-Fi. We'd like to learn more to see how we can help, along with ruling out some general possible causes:

1. You mentioned both that your iPhone becomes unresponsive and doesn't load anything from the internet while using cellular. Which issue is it? The more details you provide, the better we'll understand what you meant.
2. When did this start?
3. Sometimes unexpected behavior can be resolved with a restart: Restart your iPhone
4. Since you have a compatible iPhone model, the latest version is iOS 16.3.1. You can verify this within Settings > General > About. In case you needed it, this link shows how to first back up, then Update your iPhone or iPad.
5. We also recommend making sure that all apps are up to date: How to manually update apps on your Apple device

Cheers!