The widget detects ACF text fields to use as label. As button link it detects test and URL fields. You can choose to not have a link target.
You find it easiest by searching for ACF Button in the Elementor Search Widget … field:
Drag the following widget icon into your section to add the widget.
After adding the widget to your section/column the following settings are shown.
The fields you can choose from are found in the dropdown next to the setting “Field”. The first detected text field is chosen automatically.
Enabling lightbox will display the lightbox settings area.
See the Lightbox page for how to configure it.