WordPress users don't need to learn PHP to use, operate or manage a WordPress website.
Wordpressalready has the PHP files you need, as well as the themes and plugins so you can use WordPress without any knowledge of PHP coding. The reason why WordPress uses PHP is that PHP allows you to interact with the database and get data. So WordPress uses PHP to get things from the database and then generate them as HTML.
The various PHP tags and functions provided by WordPress are what allow this to happen on your page. No, you don't need to learn PHP for WordPress. You can create a WordPress website without knowing anything about PHP, right out of the box. There are different versions of PHP that you can install on your server, and the new PHP 7.4 and 8.0 offer significant performance improvements over previous versions. You'll notice that later chapters of Up and Running only talk about the PHP (or API) levels of WordPress.
Of course, you need the basics, but you don't need to be an expert PHP programmer to help people with Wordpress. They are the de facto industry standards in any modern PHP workflow, and you can safely say that the PHP community as a whole follows these standards. So basically, if you had to build a website using strictly a coding language, PHP would be one of those coding languages. The following snippet demonstrates the use of a plug-in header to declare a minimum version of PHP with a protection condition in the code. According to W3Techs, more than 78% of all websites that use a server-side programming language use PHP, with ASP. I have no doubt as a beginner to know that JS and PHP can probably get you a job faster than the MERN stack, I found out about this too late.
In fact, if you're interested in learning a little bit about PHP, some of these plugins can help you expand what you can do to customize your WordPress site. So in conclusion, while it is not necessary for users of WordPress to learn PHP, it is beneficial for those who want to customize their websites or create their own plugins and themes. Knowing PHP, even at a basic level, will give users more control over their websites and allow them to create more powerful websites.