It works for me here, in fact its quite annoying in that there's no way in the UI to reset the dialog, except reset workspace but that would reset everything. To turn the dialog back on you need to edit the .json preferences file.
Have a look at this file:
~/Library/Application Support/SketchUp 2018/SketchUp/SharedPreferences.json
ShowSectionToolDlg is set false when you click that box, but there's then no way to untick it apart from editing this file (or using defaults in terminal). If it has never been set that line may not be there.
[pre:2srkkumf]"Preferences": {
…
"ShowSectionToolDlg": false,[/pre:2srkkumf]
Edit at your own risk and there's something wrong anyway if SketchUp isn't writing the preference file to disk at least when you quit SketchUp.