Select text boxes with overset text

As Robert pointed out, you can select frames only on a single page or spread, so you need two scripts: one to select overset frames on a page and another to apply autosizing to all overset text frames in a document:

// Set Autosizing on overset frames

frames = app.documents[0].textFrames.everyItem().getElements();
for (i = 0; i < frames.length; i++) {
  if (frames[i].overflows) {
    frames[i].textFramePreferences.properties = {
      autoSizingReferencePoint: AutoSizingReferenceEnum.TOP_CENTER_POINT,
      autoSizingType: AutoSizingTypeEnum.HEIGHT_ONLY,
    }
  }
}

// Select overset frames on a page

overset = [];
frames = app.windows[0].activePage.textFrames.everyItem().getElements();
for (i = 0; i < frames.length; i++) {
  if (frames[i].overflows) {
    overset.push (frames[i]);
  }
}

if (overset.length > 0) {
  app.select (overset)
}