I have tried everything my iPhone 13 Pro Max detect sim and showing its name in cellular network heading but it showing no service how do I fix this few months before it working fine

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

1. Check your coverage area. Make sure that you're in an area with cellular network coverage. ... 
2. Restart your iPhone or iPad. Restart your device. ... 
3. Check for a Carrier Settings update. ... 
4. Take out the SIM card. ... 
5. Reset your Network Settings. ... 
6. Update your iPhone or iPad. ... 
7. Contact your carrier. ... 
8. Get more help.

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

Remove your SIM card from the SIM card tray and then put the SIM card back. ... Make sure that the SIM tray closes completely and isn't loose. If you use a SIM tray from a different model iPhone, iPad, or from another phone manufacturer, it might not fit properly.

If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad ...

Learn what to do if you see a SIM not supported alert.

To be able to use any SIM across the globe you must have "No SIM Restriction" against Network Provider Lock. Please refer to the pic below.

Try connecting with Wi-Fi access point and does that work ? If so, then switch Wi-Fi back off and try cellular again.

If that doesn’t work, goto Settings on the phone, then tap cellular.

Make sure the Cellular data in on. The next section down in carrier is your cellular provider, where the SIM PIN is. If you forgot you invoked the sim pin; (which I strongly recommend you do use, then every time you do a iPhone update, the iPhone will ask for the sim pin. )

This might be your case. If you hadn’t enabled this, it’s time to call your cellular provider and see if they are having issues, or if they can help.

If they don’t help, call Apple Tech support 1-800-MY-APPLE