Does US have more forest fires in Sep 2020 than average?
For now it seems to be average, at least compared to the last decade. The National Interagency Fire Center has a page with a year-to-date statistics table. You can see that so far, the values for 2020 are pretty similar (even slightly below) to the 10-year average, both in terms of number of fires and burned acres.
2020        |   Fires: 41,599   |   Acres: 5,288,247
2010-2019   |   Fires: 44,177   |   Acres: 5,761,034

Now if you go further back in time, there seems to be an upward trend. I did not compute the means, but just by looking at the numbers you can guess that there were less fires in the 80's and 90's, and about the same amount as today from the 2000's.