All you need is a product that can support being embedded via JS or an Iframe OR why not just spin up a Wordpress install with gravity forms / add Gravity Flow and link to the form pages from your WF site?
IMHO Webflow is not a fit all solution, nor was it designed to be. On the web, your visitor is just a click away from features or apps you want to share. So you can overcome limitations when needed.
Determine your requirements in detail, then find products that meet them. If you need to integrate, look at API’s available with the tools you are potentially using. Not easy but necessary.