That's true, you can't really miss what's happening with a dark mode switch -- it's not like it's a "charge me $50 extra for insurance on my shredded wheat" button.

The theme selector tho -- while rare -- IDK, that doesn't have have text -- it probably should, for the same if a11y, but you can indicate the theme with an image; the one I made for a project recently uses the image itself on the button.