How to use Vertical Tabs on ConfigEntity Form how are you?
I've created a ConfigEntity and there a Configuration Form with Fieldsets and Fields.
Example:

But now I want to change this form to Vertical Tabs, like that:

Do you know how can I do this?
P.s. It is for the Contrib project if you want to test it is:
https://www.drupal.org/project/modal_page
Use the vertical_tabs form element. There is an example shown in the API documentation for this form element: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21Element%21VerticalTabs.php/class/VerticalTabs
In short, instead of using nested fieldsets, create a 'vertical_tabs' form element as the container then put multiple 'details' form elements inside it. Each of the 'details' elements will serve as the container for one vertical tab. See the example in the API documentation for the exact syntax.