What is better for SEO and indeed for a site, a city on subdomains or a folder?

Question

Search Engine Optimization

I know that there are already many such questions, including here on the toaster, but nevertheless I decided to ask again.
The bottom line is that now there is a website, it is made extremely crookedly, some of the cities are on subdomains, some are in folders ..., no one was engaged in promotion at all ...
Now a new website is being made, the point is that firstly I want to bring everything to a single look, secondly, the main website of the online store, with 10-20 cities throughout Russia, each of these cities is a franchise, and in fact they have a separate website for each city, with the same design, but their catalog, their news, promotions, users , administrators, etc. etc. , with all this, the better the franchisees work, the more the parent company earns, as it supplies goods to these same franchise offices.
In general, I would like to hear your opinion on how to do better, primarily for search engine optimization, since the parent company naturally supports and promotes the site.

Answer 1

You need to do it on 3rd level domains, for example, moscow.beeline.ru, etc., because when you specify the regional affiliation in the webmaster panel, Yandex will see each site separately and link it to a separate city and will see it as more relevant to a particular user. Therefore, promoting many sites is much more effective than one federal site with folders for cities.