TD, Schwab and IBKR are public and do quarterly calls. Listen to their definition of active and they "usually" talk about numbers and trends. My guess in the US would be about 200,000 to 300,000.
The bigger question is what are the % performance returns of the top .10% of that grouping. -- they are stars.
My guess is that the number is dropping big-time thanks to passive ETFs outperforming even professional fund managers. Why spend time when passive means are more profitable?