I've seen WordPress server as many pages at an enterprise level with lots of traffic. WordPress is a great option, and will server as many pages as you need well with decent caching.

The creators of ElderJS have something like 50k pages that they manage, so maybe you should look at what their model is.

Otherwise use Strapi, Directus, or some other open-source headless CMS.

There's no reason to start a new project with WordPress today. It is a dumpster fire.

What's your recent experience with it that makes you describe it as a dumpster fire?

First of all, I've been working with it for 15 years. I'm intimately familiar with it.

I had sworn off ever touching it again, but I inherited 5 sites with a new client, including one that was built very recently. All are on the latest minor version of PHP and WordPress with up-to-date plugins.

With all that out of the way...

WordPress makes it impossible to do even the most basic modern software development practices. You can't easily separate your data, config, content, design, and code.

It's all mixed together by default, and you'd have to essentially create external databases or repositories to accomplish that. There was a project to try to version WordPress with git and it was abandoned for being too complicated.

There are also a million ways to accomplish the same thing, to the point where it becomes nearly impossible to know if someone's code is stored in a theme file, plugin, or database string.

Having a healthy local/staging/production environment separation is nearly impossible, especially if you need your content people or front-end designers to be able to work in parallel with anyone maintaining WordPress.

Choosing WordPress for anything today is absolutely indefensible. It's old, messy, difficult to harden, expensive to host, unnecessarily complex, and (most importantly) superseded by much better tools that weren't written nearly 20 years ago.