Sony reported their MAUs and their PS Plus subscriber numbers separately. In
a separate presentation released on the same day as these numbers were, Sony detailed that, in addition to 70 million Monthly Active Users (which are specifically measured by how many users engage with their online service by logging in, as with Microsoft), there were, at the time, 26.4 million PS Plus subscribers.
Steam doesn't give Monthly Active User numbers. Their last given number was 67 million Monthly Active Players, which they use over Monthly Active Users to make the distinction between those who have Steam installed and those who engage with the platform by playing the games. When reporting their numbers, it's how every other popular PC game service does the same - by specifying players instead of users.