Hi I see no one answered you... here's the big picture:
A forum is a heavy coded thing. It's more complicated than a CMS, way more. To begin with a forum needs a complete, solid user system. All users registered, with all the features: password management, profile management, recovering tools, moderation tools, private messaging tools. Then the forum itself, the post boards, management, publishing, list with orders.... it's complex.
Solutions to make a Wordpress a forum exist but in total honesty, developers who use it rarely do the same mistake twice. It's bloated, it's slow, it's often couter productive.
What do people use then? Some ue their own system that they code themselves, it's usually the case when their site is quite only a message board. Think Qora or StackExchange. The orhters often relies on a ready made forum system. For years PHPBB was all the rage, today it's Discourse.org. This forum we're talking on, the Webflow forum, is a Discourse forum. This illustrate well my purpose: Webflow is full of extremely talented developers, yet they don't code their own forum, because 1/ it's not their main purpose and 2/ they would likely not achieve it as well as dedicated people of Discourse would.
Can you use a Wordpress plugin on Webflow? No. Never. It will never happen even in a distant twisted parallel universe. (well maybe in a parellel universe where chicken are pink with 10 feet legs, Nascar racing runs on a vertical looping and Donald Trump is president of the Unit... oh wait...) Ok no it's not happening, not the same software and not the same technology.
Can you use a forum system that's not Webflow within a Webflow site? Yes. You can EMBED a whole site within another, using HTMLs' iFrame object. It's like a window showing another site from your site. If setuped well, it can be hardly noticeable.
You can also setup the forum on another domain like forum.yourdomain.com, and make the header look like your site, exaclty like Webflow does here.
Hope this gives you a better understanding of what's possible and what's not.