did some back of the napkin math with what the apollo developer has said publicly. each user makes 10,000 api calls a month and there are 2 billion calls per month which means 200,000 MAU. Reddit has an MAU around 500m users.
The article says the average Apollo user makes 345 API calls a month. Using your number of 2 billion calls per month, that’s more like 5.8 million MAU. Still around 1 percent of Reddit’s MAU.
EDIT: Oops, that’s per day! Your math is right, please ignore.