After waiting for a while, the status info in QFlash changes to “[COM0]Download fail[Open port fail]!” which is very strange because I don’t even have a COM0 on my computer. All the available COM ports are shown in the device manager screenshot.
I tried on a different computer, and it worked flawlessly. I borrowed an old laptop from the office for flashing, and gave up on trying to solve the problem on my main dev machine.