Flexible Content fields in ACF are automatically detected by WP All Export and added to the ACF section in Available Data.

ACF Flexible Content fields enable a simple block-based editor that allows using layouts and subfields to organize the data. Similar to a Repeater field, any field can be added to a Flexible Content field as a child.

This Flexible Content field has 1 layout that contains 3 subfields, a Text field, an Image field, and a Color Picker field:

When more layouts are added, each exports its own set of columns. The above field exports the following:

• Flexible Content__0_text: Exports the string from the text field.
• Flexible Content__0_image: Exports the URL of the added image.
• Flexible Content__0_color: Exports the HEX code selected in the color picker.

Here's what that ACF export file looks like: