If you are considering switching from a subdomain to a subfolder, you should read this.
Does Switching From a Subdomain to a Subfolder Improve SEO? Case Studies & Experts RoundUp
The subdomain vs. subdirectory question has been around probably ever since Google first appeared. People ask themselves if having one or another affects SEO. The popular belief is that switching from a subdomain to a subfolder of the root domain will help increase the overall rankings of your website.
https://cognitiveseo.com/blog/16687/subdomains-vs-subfolders/
