If I understand what you want to do, I think the best way would be to
drag your mouse across the text to highlight it and then copy the text.
You can then delete the text box and paste the text into something else.
In PowerPoint, all text is contained in some form of text box (either a
regular text box, a text placeholder, or another shape with a text
area). Unlike Word, there is not general text area so you have to have
the text in something.