How to deactivate the text, that appears, when you hovering over topbar tabs? [closed]

This is most likely configured as a title attribute somewhere in the template files, or in a functions.php-like file. I would first find where they are configured, and try to change them from there.

Otherwise, you can still use jQuery to remove the title attributes with something like this:

jQuery( document ).ready(function($) {
    $("header nav a").attr("title", "");
});