There is no strict limit on the number of users a WordPress site can handle. Wordpress dominates 65% of CMS market share and for good reason. It's easy to use, scales to your needs and is completely free to use. Can WordPress manage millions of users? WordPress is nothing more than a type of software that can be used to build a website.
This means that WordPress itself does not limit the number of users who can visit a website at the same time. However, there are some essential steps that must be taken to ensure that a website is not blocked when too many people try to visit it. You mean a private blog? You can add 35 users to your private blog and you can purchase the Unlimited Private Users upgrade if you want to add more. If you are referring to a public blog, then there is no limit to the number of official users you can add to your blog, adding users/user roles.
WordPress is a content management system or CMS. It is basically software that is loaded on a server. There are no user limits for WordPress. The only user limitations are determined by server capacity, disk space, and so on.
There are several reasons why you would want to change your hosting provider and WordPress gives you that kind of flexibility. There are literally hundreds, if not thousands, of large companies using WordPress. I'm not going to list them all here, but surely you can find an inexhaustible list by doing a simple Google search. Yes, WordPress can handle a lot of traffic.
WordPress itself has no limits on the amount of traffic it can support. However, your choice of web hosting and on-site performance optimizations can make or break your site's ability to handle heavy traffic. Assuming that all your users have at least 1 role, they have a wp_capabilities entry in the user_metadata table with a serialized array of roles. As wordpress doesn't have much dynamic content, this can be achieved with some nginx and cloudflare reverse proxies.
Transferring a WordPress website from one host to another, although it's not very simple, is quite simple. Again, just like the number of posts your WordPress can handle, the amount of traffic your WordPress site can handle will depend on your server and your server resources. The question should be how many users can handle the php-mysql stack instead of WordPress, since WP is built on those 2 main technologies. As you can see, WordPress can not only handle a large database, but it already handles some of the largest databases on the Internet today for some of the largest companies in the world.
So if you're worried that WordPress can handle your database, your worries are out of place. My job is mainly to support self-service oriented CRM software on WordPress, and I've worked on at least one installation of this one that had over a million contacts (although it was on Drupal, but the same CRM software), and I would highly recommend it against this. WordPress can handle absolutely heavy traffic and, in fact, many of the popular sites you frequent are probably powered by WordPress. In general, it is very easy to get into a situation where long-running queries have created locks at the table level, and that can stop access to the database and significantly slow down the system, even when there is only one user accessing the system.
In the end (despite all the developments), WordPress is just blogging software created for people with very little knowledge of web development. With WordPress, you have much more control not only of the theme you use, but, more importantly, of the hosting service provider on which you choose to host your website. Every time someone comes to your site, WordPress has to query the database to get the necessary data, compile it together, and create your page on the fly before the user can see it. Alternatively, you can install ElasticSearch on the server and use the ElasticPress plugin or another plugin that integrates it into WordPress to speed up such searches.
Handling large amounts of data over the Internet has much more to do with where the WordPress site and its servers are hosted rather than with the content management system (CMS) of WordPress itself. . .