Using query provided by ArtOfCode I made the following two graphs. They show unique users weekly over the past 10 years (for Stackoverflow.com, not the entire network). One is a total number of users and the other are active users with at least 10k reputation. Not really what I was looking for, but I think they show useful information too. The spike does correlate with the spike in new accounts being created that CEO talked about.
We can see that participation has risen in the past few weeks. It's difficult to draw any hard conclusions because some of it could be due to the fact that the query doesn't consider deleted posts. However, it does look like we now have almost 90k unique users active each week.
The following graph shows the participation from users with a considerable amount of reputation (>10k). We should be observing an upward trend, because more and more users should cross the 10k threshold, but instead we see a steady downward trend. Reputable users are decreasing their activity. Neither dark mode nor any of the Meta drama has impacted their activity. It looks like less than 5000 10kers are active every week.
If both trends continue we could see a considerable decrease in the quality of the content posted on the site. The reason why I compared it against 10kers is that these are the people who have both close vote and delete vote privileges. They know the rules and what is good on-topic post and what isn't. If all we get is more new users and less old users then there will be fewer active people who can curate the content and take necessary actions.
With increasing noise, there will come a time when proper high-quality content will be more difficult to find and all users will start looking for greener pastures.
Here is my plea to Stack Exchange:
Please, do not focus on new users coming to the site. Focus on retaining the active user base. This is the way to ensure steady and sustainable growth.