These are top and recommended Custom Form Builder For Magento 2 Ecommerce

1) As ease-to-use as Google Form, Magento 2 Form Builder is a powerful form creator tool. 20+ input types, dynamic Drag n Drop, and customizable backgrounds are dedicated to supporting extensively in creating forms.
Link: https://landofcoder.com/magento-2-form-builder.html

2) Itoris: Advanced and powerful SmartFormer Gold will extend the default Magento 2 functionality and take your custom forms to a new level
Link: https://www.itoris.com/magento-2-form-builder.html

3) Amasty Form Builder: Create web forms of various types to effectively collect customer info. Use a handy constructor to generate multiple forms in no time and customize each form to meet your needs
Link: https://amasty.com/custom-form-for-magento-2.html