Custom code plugin does not work

I usually create a custom function plugin in the webs I make so as not to overload the site with plugins when what I need is something simple.

I’m starting a new site and my plugin doesn’t work. However, I put the code in the functions.php of the Astra theme if it loads.

Why? I tried something simple to confirm that it doesn’t work and this code:

<?php

function saludar(){
    echo "Hola";
}

add_action('astra_entry_after','saludar', 10, 3 );

Creating it in the personal plugin does not work and pasting it in the functions.php does.