Need to add localStorage to it, but also an option to re-enable in the user settings in case you accidentally closed it and actually do want it activated.
In any case, noticed OP is on an iPad, so made some changes that might work for him
I use the nodebb-plugin-night-mode to switch off the light but noticed that with the Cerulean Skin many buttons show with a glowing white background color which of course is not compatible with a dark mode theme (mod).
It works just fine with Cosmos and some others skins I tested. It is possible to get that fixed with Cerulean ? I think that skin just looks best on NodeBB.