"We can't save the customer" error after Migration - Magento 2.3

Yes,I am not sure about it. but it is clear that the issue is happening for some custom attribute.

Some of the attribute's frontend_input field value is label and that is wrong.magento does not have this type of frontend_input type field.

So, you have to find that attribute, first goto database and then eav_attribute goto run below code:

SELECT * FROM eav_attribute where frontend_input = 'label'

You have to delete those attributes .But its means you willbe lost value of this field of catalog product/category/customer entity