Earlier this week, final 2019 enrollment numbers for Obamacare were released. This is for states on the federal exchange only:

This means that 2019 ended up about 4 percent lower than 2018. However, there are several state exchanges, including big ones like California, that haven’t closed enrollment yet. When you account for this, and also for some Medicaid expansions that probably cannibalized some customers from the exchanges, it’s likely that net enrollment this year will end up down by 1-2 percent or so.
Over at Vox, Dylan Scott summarizes a few theories about why enrollment declined, but to me this looks like just a random fluctuation, especially since 2018 was a year of strong economic growth—which means more people got jobs that offer health insurance and therefore left Obamacare.
Overall, then, Obamacare is doing fine. So far, the loss of the individual mandate doesn’t seem to have had much effect, though it’s a little early to say that with any assurance.