sold my iphone 13 promax and i can

Use the steps in this support article to remove your personal information from a device, even if you don't have it anymore. --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Use a browser and sign into iCloud and your Apple Id. Unless something has changed, there is a way to remove the device once you have logged in. I had the same problem last year.