.text() is meant for retrieving text from an element. You don't have any DOM elements here, only a plain array composed of strings.

The error is thrown because getText (which jQuery calls when trying to get the text of an element) does

getText = Sizzle.getText = function( elem ) {
    var node,
        ret = "",
        i = 0,
        nodeType = elem.nodeType;

    if ( !nodeType ) {
        // If no nodeType, this is expected to be an array
        while ( (node = elem[i++]) ) {
            // Do not traverse comment nodes
            ret += getText( node );
        }
    }

resulting in infinite recursion.

While you can just refer to this in strict mode to have it refer to the string being iterated over...

'use strict';

var arr = ["janusz", "renia"];
$(arr).each(function() {
  console.log(this);
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

It'd be far easier to ditch jQuery entirely and use plain JavaScript.

var arr = ["janusz", "renia"];
for (const item of arr) {
  console.log(item);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js"></script>

or

var arr = ["janusz", "renia"];
arr.forEach((item) => {
  console.log(item);
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js"></script>

or

var arr = ["janusz", "renia"];
for (let i = 0; i < arr.length; i++) {
  console.log(arr[i]);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js"></script>

If you're new to programming, I'd personally recommend only using jQuery when you need to, and not trying to use it for absolutely everything (which is an unfortunately common paradigm).