I know they allow you to export your code and if you're paying for it, you can use it without any attribution. So I don't see any reason off the top of the head where why you couldent use if for foss stuff.
Discussion
That’s along the lines of what I was thinking. I guess the downside from a foss perspective would be if someone wanted to fork your project and play with the design, it would require a webflow subscription to do so.
Maybe that wouldn’t matter all that much. They could always just edit the design by hand.