i lost my iphone 12 pro max

1. If your iPhone, iPad, or iPod touch is lost or stolen - Apple ...
2. Find the serial number or IMEI on your iPhone, iPad, or iPod ...

You may use a web browser to get Serial Number and IMEI Number. You cannot track using iMEI number. but you may need it so keep it handy

Don'ts

If you remove the device from your account after you erase it, Activation Lock will be turned off. This allows another person to turn on and use your device.

Do's

• Mark As Lost.
• Erase your device.
• Apple Care+ :- file a claim for your lost or stolen iPhone. (If you had Find My enabled)

Did you enable Find My?

If you didn't turn on Find My [device] before your device was lost or stolen, it can't be used to locate your device nor you can use the IMEI number for tracking the device.

The best action would be to Change your Apple ID password and change the passwords for other internet accounts on your device. This can include email accounts, Facebook, or Twitter, etc...

Apple Support Community Forum

This is Apple Support Community forum, for a user to user interaction for information & idea sharing between users, if need be, extend support on technical knowhow in handling Apple products from a more experienced fellow user, This is not the right forum to discuss with Apple Inc.