analytics.usa.gov shows information about how many people are "on government websites now"—about 350k at the time I checked.
There were 5.09 billion visits over the past 90 days.
The most "popular" website run by the government is USPS, by far: tracking mail and delivering results of Covid Home Test kits. Scientific sites are up there, such as NIST and NASA, and various other Covid info pages. And then we get to the 'here's the bad news we promised" government sites like the IRS and the National Weather Service.