How can I find or blacklist my lost iPhone 12 Pro Max using IMEI number?

Blacklisting is done by the cellular carriers.

Report it to your carrier.

You can not track the location using the IMEI. Technically, the carriers can, but they will not do so without a court order requiring them to. That usually only happens if someone’s life is in imminent danger.

Contact your carrier to ask them to blacklist the phone.

Apple does not use IMEI to locate the phone. Your carrier does.....but they will only normally do this in cases of missing persons or a similar emergency. Even then, the carrier will require a court order to begin the process.

If your iPhone or iPad is lost or stolen - Apple Support