I restarted my PC, disabled Avast for 10 mins and reran the Docker For Windows installer successfully. However, when starting Docker For Windows, it failed again so I tried to submit a crash report. Whilst that was running, Avast again detected powershell.exe as a threat again and automatically moved it to the virus chest. I think that's what I was doing the first time Avast detected powershell.exe as a threat - sending a crash report in Docker for Windows.