It's neither of these options in this false dichotomy.

100M people signed up and did at least 1 task. Then, most likely some % of them discovered it was a useful thing (if for nothing else than just to make more memes), and converted into a MAU.

If I had to use my intuition, I would say it's 5% - 10%, which represents a larger product launch than most developers will ever participate in, in the context of a single day.

Of course the ongoing stickiness of the MAU also depends on the ability of this particular tool to stay on top amongst increasing competition.