Placing a Button Module or a Text module over an Image module can be achieved using the Position option, which can be found in the Advanced Tab > Position.
Note: All elements in Divi are positioned relative to the page
Considering that all modules are positioned relative to the page, we can use the Position option to change the position to absolute for the Text or Button modules.
Building the Layout
Insert a Row with 2 columns - this will work for any number of columns
Insert the Image module and set the image you want to use
Insert the Text module - this should be placed in the same Column as the Image module
Edit the Text module's settings, go to Advanced Tab > Position, and set the position to Absolute
Use the Location option to position the Text module over the Image module
The same steps can be followed for the Button module as well.
Note: Using the Position Absolute on the Text module, selecting it for further edits in the Visual Builder will be impossible.
We can use two different methods to be able to select and edit the Text module once its position has been changed to Absolute:
Use the Divi's Layers View
Use the Wireframe