Most popular form builders use their own custom visual form builder that’s not integrated with Gutenberg. These forms are usually then added to your posts/pages with shortcodes. Some form builders have a dedicated Gutenberg block.
I haven’t seen any form builder integrated with Gutenberg in a way that’ll let you use Gutenberg blocks to add elements to the form. But I don’t use forms that often so maybe somebody with more experience with forms knows about such form builder.
I’d suggest you to choose a form builder that fits your needs/budget. If you can use shortcodes to add the form to your posts/pages, then you shouldn’t have problems using it with Cwicly. Take into consideration that not all form builders allow you to customize all aspects of the form. In such cases you’d need to apply custom css to achieve the design you need.
A Cwicly form builder is planned . You might be interested in this this feature Cwicly Form Builder.