Our recommended WordPress plugin for creating Custom Fields is the Advanced Custom Fields plugin.
Using custom fields, we can hide/show Sections/Rows and Modules using Divi's Display Condition feature.
Setup
Install and activate the Advanced Custom Fields plugin.
Create your first custom field.
Creating the first custom field
Go to the ACF option in the WordPress dashboard and click on Field Groups:

Click on Add new button (at the top):
Give the Group a name - it can be anything you want.
Add at least one field by choosing the Field Type and setting the Field's Label:
Note: In the above example, I chose to use the text field type, and the field's label is My Custom Field. The ACF plugin will automatically fill in the Field name value - so you don't have to worry about that.
Decide on which post type (Page, Post, Product, Project) the custom field should be used.
Click on the Save Changes button (top right corner).
Using the ACF Field in Divi's Display Condition option
Once at least one field is created, we can use it inside Divi's Display Condition to determine whether a Section/Row/Module should appear based on the Custom Field's value.
The Field Group was set to show on Page in the following example. First, we must create a new page or edit an existing one.
The ACF field will be displayed at the bottom while creating a new page or editing an existing page.
Set the value of the ACF Field
Enable the Visual Builder
Edit the element (Section/Row/Module) for which the Display Condition should be used
Go to the Advanced Tab and open the Display Condition option group
Click on the plus icon to add a new condition
Choose Custom Field
Select the custom field name
Set the Display Condition
If the condition is true, the element (section/row/module) to which the Display condition will be applied will show.
If the condition is false, the element (section/row/module) to which the Display condition is being set will not show.
We also have a great video that explains in detail how to create/set up and use a custom field with Divi's Display Conditions, you can see it here -> https://vid.divi.tech/xzzVsC25.