Mobile data update required

Next step would be to set it back to factory settings, using your computer. Make sure to create a backup before you start. Your computer will install a complete new version of iOS, including all needed updates.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

As a first step, set it up as a new iPhone, without using the latest backup.

Then check if using mobile data is possible.

If it is, restore your data form the backup.

You can update your carrier settings manually, follow the steps in this article to do so:

Manually update your carrier settings on your iPhone or iPad - Apple Support

If you are using a PC, did you make sure that the newest version of iTunes has been installed?

Is your SIM card working and supported by your provider?

The Activation Lock on your iPhone has been disabled?

If your SIM card has been damaged, you should contact your provider to get a new one.

You're welcome 🙂

After all you have tried, this could also be hardware related.

To find an Authorized Apple Service Provider next to your place, you can use this link:

Apple - Find Locations