I can only open websites with wi-fi on in iPhone

Possibly you have a hardware failure, but lets try some more.

First try a forced restart

https://support.apple.com/en-gb/guide/iphone/iph8903c3ee6/ios

 Secondly do Settings, General, Reset, Reset network settings.

If that does not help the  next procedure would be to backup then restore your device to factory, and setup the device without restoring a backup, to see if the issue is replicated. 

Then restore the backup. 

If you need to send the phone in for repair then backing up and restoring to factory would be needed anyway.

Here is a guide for those steps

Backup and restore (I recommend the computer method if you have one)

(1)How to back up your iPhone, iPad, and iPod touch – Apple Support

Remove SIM PIN if you have set one

(2) Restore your iPhone, iPad, or iPod to factory settings – Apple Support

Set up as new from the Hello Screen without restoring backup. Test if the problem still exists

If the problem goes away in the newly set up phone then suspect settings or apps, and in particular VPNs and so-called security apps which should never go near an iphone.

If the problem remains then arrange a repair including details of these tests.

https://support.apple.com/en-gb/iphone/repair/service

(3) When your phone comes back Restore your iPhone, iPad, or iPod touch from a backup

Is your cellular/mobile data turned on in Settings?

Does your cellular account have credit?

If it is showing bars of 4G then it should connect.

Or is it showing No Service?

Have you installed any security apps?

I would ignore other people's problems unless they offer successful remedies.

What happens when you try and go to a website?

What is the cellular speed if you install a speed tester app like Meteor?

forgot to add can you try another SIM?