Here is the SEO Difference Between Subdomains and Add-On Domains

If you have been doing search engine optimization for a while, you have probably heard certain guidance about hosting content on subdomains. More than likely, this guidance recommends against the use of subdomains for SEO, but you should not confuse this with add-on domains. Let's break down why subdomains do not work in terms of SEO:

Many of your site's functions involve hosting functions such as indexing and searching, which includes serving up links and information to visitors of your site. Do not ignore this if your site only has a few pages, for example for news related to your site. Instead, include a URL in each page (such as /news), followed by the page's title, or "content" field, which should include links to the "story" page's data about the information in the text.

If you are indexing your web page for search engines, you should try to put all relevant content and structured data on the principal domain. This does not mean your subdomains will never be indexed by Google, but they will become secondary to the crawlers. You would be better off with redirecting to the main site, and this is where you can create the appropriate categories.

It is important to note that subdomains are not the same as add-on domains that share the same IP address. If you have a shared cloud hosting plan where it makes financial sense to purchase a new domain name that will be hosted under the same plan, you will have less to worry about than if it was a subdomain. Think about a Shopify online store whereby you go the express route of choosing an available domain name offered by the platform; in this case, no subdomain is created because a new domain is added under what seems to be a static IP address.

If an e-commerce site share the same IP with hundreds of other Shopify stores, this will not have any bearing with regard to SEO. As for hosting a store on a subdomain, you only have to give it a few days for the Google crawler to visit and index, but you can always link to it internally from the main site. For more information click here https://www.reddit.com/r/SEO/comments/meqtg6/ishostingonasubdomainholdingme_back/.