Mobile Data Update Failed

After restarting my iPhone X as usual, after unlocking it with my passcode, I did not receive the usual prompt to enter the code for my SIM card.

What's more is that no service is found, the bars at the top keep looping/trying to search for service.

After a while, a message popped up stating "Mobile Data Update Failed".

When checking under Settings -> Mobile Data, it informs me that an update is required to use mobile data.

After restarting, the situation is unchanged (again no SIM pin prompt, either) and this time, checking under Settings -> Mobile Data, the page is entirely blank. There are no toggles, no sub-menues etc. Just like with this user https://discussions.apple.com/thread/251288419

Following the link under "learn more", I conducted a full re-install of iOS 15.3 via iTunes on my PC. The issue persists.

When restarting the phone without a SIM card in the tray, the issue persists unchanged.

When inserting the SIM card into another device, the SIM card is recognized and the other device can be used normally.

I would appreciate any input!