How to create a simple form to redirect the user to entered URL?
Have a look at the Rules Forms Support module. Some more details about it (from its project page):

Rules Forms Support provides a Rules based method for controlling forms and their elements. The module can be used to alter any form provided by Drupal core or contributed modules. Change element titles, descriptions, weights, and more, or validate form data and set form errors. Rules forms saves time and cost by affording site builders the ability to monitor and alter forms without the need to implement a custom module.
For help getting started with Rules Forms Support, please see the module documentation.
Features

Activate events for form creation, validation, and submission on a form-by-form basis.
Target individual form elements or the entire form in conditions and actions.
Manipulate the attributes of a form element like title, description, weight, and more.
Validate the values of form elements during form validation.
Set form errors when rule-based validation fails.
Redirect users to a different page upon viewing or submitting a form.
Examine the attributes of elements in active forms with the element inspection tool.


Especially the &quot;Redirect users to a different page upon viewing or submitting a form&quot; should help to address your question.