The Save Text item is available in the Text menu and via the Insert and Extract Text button on the collection toolbar, except when the Recycle Bin tab is active.
Select the Save Text item to store the selected part of the text of the active clip into a text file.
If you want to save multiple clips into one or more text files, use the Export Collection item in the Collection menu instead.
See Editing Clips and Text to learn how to use AceText.