TL;DR Strictly speaking yes it would be possible to do this. But there are many drawbacks, it’s hard to achieve a quality result, and this isn’t an efficient way to work. Just let Webflow do what it’s great at and leave web apps to dedicated frameworks.
It’s true that Webflow does produce relatively clean code - as long as what you input is sane. Webflow isn’t magic, but if you are using sematic elements and tags, and good HTML and CSS structure then you will get a good output. Basically “good in = good out” and “rubbish in = rubbish out”.
However, clean website code is not the same code used by most modern front end applications. Websites don’t need to manage state, whereas apps do. This is a major difference and requires a different approach to displaying static information in on a webpage (pretty much what Webflow does).
You also need to consider a developer’s workflow, versioning, deployment and all the other things that go into making a web app. I actually wrote a whole Medium article on this topic. It goes into a lot of detail, but you will get some good insights there.