Is it correct to consider static methods global along with their classes?

Question

PHP

Hello! I read the documentation, but I still don't understand. If I create a class with static methods and a static parameter like this:

class Speedbar{

  private static $data = [];
  
  public static function getData(): array
  {
    return self::$data;
  }
  
  public static function setData(array $data): void
  {
    self::$data = $data;
  }
  
}

Will I be able to call and change it from any part of the web application? (taking into account the autoloading of classes)
I tried and indeed, wherever I change the data parameter , in any php file it remains already changed.
Then it is not clear why singltone is needed if the class is already unique using only static methods

Answer 1

Regarding Singletone.
Static methods cannot be declared in an interface, hence you are tied to a specific implementation. There is no such problem with singleton.
UPD : as indicated in the comments, it can still be done.
Static methods are harder to code for tests. With a singleton, everything will be easier here too.

Answer 2

Then it is not clear why singleton is needed if the class is already unique using only static methods

A very old question.
The singleton has nothing to do with the state of the class, only the number of instances. A singleton can only have one. This is such a crutch for procedural programming, for those who do not know how to OOP.
With normal OOP, a singleton is not needed, since the programmer is able to control how many and what objects are created for him, and not try to create a new object if the desired one has already been created.

Is it correct to consider static methods global along with their classes?

Correctly. This is shitty code, with very few exceptions.