Based on how confusing I find my iPhone mute toggle button, I am leaning toward the idea that buttons that have no text (are they always toggles?) should be different from text-based buttons. Icon toggle buttons seem to make more sense to me when they are, as you say, showing the current state. Then again, play/pause, if it’s one button that toggles, would make more sense to me in the normal way, where the play button means I want to play, not that it’s already playing.
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