A reader pressed the switch once and the site stays that way

Under General → Visitor Preference, set How long to Until their device or your schedule next switches. With a schedule, a press then lasts until the schedule's next start or end, even if the reader has no page open at that moment. With no schedule and Default Mode on Auto, it lasts until they open a page while their phone or computer is set the other way from when they pressed; a phone that switches and switches back while none of your pages is open leaves it as it was. After that the site follows the schedule or the device again. It is the default on a new site; a site that had the plugin before keeps Until they change it and its Dashboard offers the change.

A reader who wants dark all the time on a phone that switches by itself will need to press again after each switch. With Default Mode set to Light or Dark and no schedule, nothing switches, so a choice stays until it is changed.

To let readers go back to automatic whenever they like, place the Light, Auto and Dark switch (the block's Style, [dark_mode_switch style="choice"] or the menu item): Auto forgets their choice.