You can do this via python an its win32com.client. This loop will print out all text from all slides of Test.pptx.

import win32com.client

ppt_dir = r'C:\Users\Documents\Test.pptx'
ppt_app = win32com.client.GetObject(ppt_dir)

for ppt_slide in ppt_app.Slides:
    for comment in ppt_slide.Comments:
        for shape in ppt_slide.shapes:
            print(shape.TextFrame.TextRange)

Result: This is a test

Take this as a starting point, depending on what you want to do with the extracted text.