Ok. There's just no good way to answer this question. It varies from day to day, and we'll even have experienced park-goers here
in the same park on the same day who will give you two different answers. Crowd perception is a function of perspective, previous experiences, and also just where you are in the parks at certain times. One person's "low crowd" day is another person's "packed."
HAVING SAID THAT, I'd say that in general, weekends are busy and weekdays aren't too bad lately (with some exceptions). Specifically, I've been four times in September and will give you my impressions:
Wednesday, Sept. 1 - visited from 8-11pm. The parks were pretty deserted. (I was able to get a Webslingers Boarding Group at 8pm, which is pretty unheard of.) It seemed quite empty, and by all accounts, that had been true all day.
Friday, Sept. 3 (First day of Halloweentime) - visited both parks from 4pm until 10:30pm - This was "moderately crowded," with most people there to see Halloween stuff. Ride waits were pretty low - we got on Haunted Mansion Holiday in less than 15 minutes around 4:30, which surprised me. By the time the Halloween fireworks started, though, Main Street was an absolute crush of humanity, as one would expect.
Monday, Sept. 6 (Labor Day) - visited DCA from about 8:30am until about 3pm. I'd describe this day as "pretty crowded." While ride waits were still quite reasonable, walkways were congested and food service was challenging. Long lines for food, or long waits for mobile order windows/pickups. Animation Academy at 2:00 was "full" by 1:50. That's rare.
Friday, Sept. 10 - visited DL from 4-6:45pm - This was weird. Ride wait times were SO LOW. We literally walked directly onto Star Tours at 5:45pm. But the parks didn't "feel" empty. It was like the parks were normal crowds, but no one was on the rides? I can't explain it.
As the Magic Key program ramps up and Disney adds
Genie+ at some point, things could change quite a bit. But that's how I'd describe crowds recently.