If you want to get CollectionType to work, you can:

1. Copy-paste some jQuery from How to Embed a Collection of Forms. That requires understanding of Customize Form Rendering.
2. Depend on third-party implementations such as phiamo/MopaBootstrapBundle, braincrafted/bootstrap-bundle or ninsuo/symfony-collection. Those libraries aren't that well maintained (see Docs are down braincrafted/bootstrap-bundle#468 and MopaBoostrap Documentation / Future of MopaBootStrap phiamo/MopaBootstrapSandboxBundle#47)

I'm now using MopaBootstrapBundle but I want to get rid of it and use Symfony's own Bootstrap form theme instead. The bundle isn't well maintained and doesn't work with Bootstrap 4: phiamo/MopaBootstrapBundle#1222

I think using CollectionTypes should be easier. Customizing Form Rendering shouldn't be needed to get it working. I've got an application with 100+ forms and use custom templates rarely, because most Form types work perfectly with the default templates.