Do subdomains matter for website promotion?

Question

Search Engine Optimization

The question is probably overused. But I really had a snag. Why subdomains are needed, I know perfectly well. A vivid example is subdomains by region like tula.site.ru, orel.site.ru, etc. And it's not about that.
Here’s what I have:
when checking the number of site pages in the Yandex index with the site:domen.ru query, it returns several hundred results, 90% of which are various types of subdomains, including both working sites with product catalogs and non-working pages with a service information like "the domain is parked in such and such". At the same time, working subdomains have completely different topics (I suspect that these are old projects of clients of the company - the owner of the original site), which do not coincide with the main domain (building materials store, cosmetics store, etc.)
Question: what to do with these subdomains? Do I need to do anything at all, or do they have no meaning for the main domain and do not affect its promotion in any way and only create difficulties when checking the number of pages?

Answer 1

You can do nothing with these pages. They do not affect the main domain, as these are separate sites.
To be completely calm, you can hang robots.txt on all subdomains with a ban on indexing.