Which URL/Domain Structure Should be Considered for SEO?

Hello BHW,
I have one clients projects into B2B engineering services looking they have different verticals into Manufacturing, Services and Ecommerce Shopping.
But the project which I have got into engineering services which they provide to automotive and manufacturing.
But I'm quite confused about the SEO part. Need your recommendation

Which URL structure would be the best considering for ranking the website either
A Subfolder or Subdomain
example
website.com/engg-services
or
engg-services.blackhatworld.com

As per example above my main concern is rank for their pages under engineering services not pages under the main domain(such as website.com/manufacturing and website.com/shop)

Since content of 1st and 3rd business vertices are quite different from 2nd vertical(Which I got the project).
With different social media accounts for each verticals not interlinked each other at all.

Let me know in such cases whether a subfolder or subdomain would be best to start? In such cases.