Run the following in powershell.
# This script will remove grouping from all possible views of the Downloads folder.
# The change is applied to the current user's profile only.
# Warning: ALL folder views (except Downloads grouping) will revert to Windows defaults!
# This is a minimal solution. To set ALL default folder views, use the free tool WinSetView.
$RegExe = "$env:SystemRoot\System32\Reg.exe"
$File = "$env:Temp\Temp.reg"
$Key = 'HKLM\Software\Microsoft\Windows\CurrentVersion\Explorer\FolderTypes\{885a186e-a440-4ada-812b-db871b942259}'
& $RegExe Export $Key $File /y
$Data = Get-Content $File
$Data = $Data -Replace 'HKEY_LOCAL_MACHINE', 'HKEY_CURRENT_USER'
$Data = $Data -Replace '"GroupBy"="System.DateModified"', '"GroupBy"=""'
$Data = $Data -Replace '"SortByList"="prop:System.DateModified"', '"SortByList"="prop:System.Name"'
$Data | Out-File $File
& $RegExe Import $File
$Key = 'HKCU\SOFTWARE\Classes\Local Settings\Software\Microsoft\Windows\Shell'
& $RegExe Delete "$Key\BagMRU" /f
& $RegExe Delete "$Key\Bags" /f
Stop-Process -Force -ErrorAction SilentlyContinue -ProcessName Explorer