You can create user-defined customer attributes using Patch Data in Magento 2.
If you have some requirement to show customer attributes to only a given website in multi website setup.
This article displays customer attributes for specific website levels.
Let’s hope you have created a simple module,
Just create a new Data Patch file under the path, app/code/<Vendor>/<Modulename>/Setup/Patch/Data/CustomerAttributes.php
We have to create a new attribute called ‘mobile’ and display it on the customer registration page, and customer edit page.