Subdomain or subfolder, which is better for SEO? John Mueller answers this question on Google's SEO Snippets video series.
Deepak from India asks us subdomain or subfolder, which one is the most beneficial for SEO. Google web search is fine with using either subdomains or subdirectories. Making changes to sites URL structure tends to take a bit of time to settle down and search so I recommend picking a set up that you can keep for longer. Some servers make it easier to set up different parts of a website as subdirectories, that's fine for us. This helps us with crawling since we understand that everything's on the same server and can crawl it in a similar way. Sometimes this also makes it easier for users to recognize that these sections are all a part of the same bigger website. On other servers using sub directories for different sections like a blog and a shop can be trickier and it's easier to put them on separate subdomains. That also works for us.
You'll need to verify subdomains separately in Search Console, make any changes to settings and track overall performance per subdomain. We do have to learn how to crawl them separately but for the most part that's just a formality for the first few days.
So in short use what works best for your setup and think about your longer-term plans when picking one or the other.