I have a high authority static site that ranks really well in google. I want to add a blog to this site in a SUBFOLDER, (domain.com/blog) with the main motive of piggybacking on this sites existing authority, and using subfolder structure in my experience works well for this purpose. (especially as opposed to subdomains blog.domain.com or a completely separate new domain)

But, the niche of the existing site and the new blog are not very closely related, one is beauty and the other would be weddings.

I would like to hear some expert opinions on whether this is a good idea, or should I just create a completely new site?

Any drawbacks to using the subfolder for the new blog when the topics are not closely related?

Thanks all!