In the old Memory-Map Navigator, text overlays were a special kind of overlay. In Memory-Map for All, you can achieve a similar result using marks.
Edit the mark, click Icon, and change the icon to "Name". The mark now displays the name of the mark as text on the map instead of using an icon.
To display longer text, you can enter the text as the Note in the edit mark dialog. You can enter multiple lines of text. Then tap Icon and select "Note" as the icon type.