3rd party (so unreliable) numbers suggest they lost around 6% user engagement. I woukd guess that serving adds to all the people that switched from 3rd party to official apps probably made up for it in the short term.
Once upon a time, reddit was an open-source platform. Never again it has the same face when it decided to close the sources, then the UI changes, then the ads, then the API charges. All of those are for the profits of them, not of users'.