Unfortunately, the threading setting is a baseline, not a universal setting. That is, the setting is applied to NEW folders after the setting has been set. If you have already created folders, then you would need to reset them after the baseline in config editor was changed. There are simple keystrokes that allow you to set one folder and then apply those settings to all other folders in an account. I agree that such a setting is desirable, but it isn't. That request has appeared almost daily since threading became the default in 2022.