Install WinGet (.ps1)! (on x64 systems)

Install-WinGet.ps1

$ErrorActionPreference = "Stop"
$apiLatestUrl = 'https://api.github.com/repos/microsoft/winget-cli/releases/latest'
$tempFolder = $env:TEMP

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
$WebClient = New-Object System.Net.WebClient


function Update-EnvironmentVariables {
  foreach($level in "Machine","User") {
    [Environment]::GetEnvironmentVariables($level).GetEnumerator() | % {
        # For Path variables, append the new values, if they're not already in there
        if($_.Name -match 'Path$') {
          $_.Value = ($((Get-Content "Env:$($_.Name)") + ";$($_.Value)") -split ';' | Select -unique) -join ';'
        }
        $_
    } | Set-Content -Path { "Env:$($_.Name)" }
  }
}

function Get-LatestUrl {
  ((Invoke-WebRequest $apiLatestUrl -UseBasicParsing | ConvertFrom-Json).assets | Where-Object { $_.name -match '^Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.msixbundle$' }).browser_download_url
}

function Get-LatestHash {
  $shaUrl = ((Invoke-WebRequest $apiLatestUrl -UseBasicParsing | ConvertFrom-Json).assets | Where-Object { $_.name -match '^Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.txt$' }).browser_download_url

  $shaFile = Join-Path -Path $tempFolder -ChildPath 'Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.txt'
  $WebClient.DownloadFile($shaUrl, $shaFile)

  Get-Content $shaFile
}

# Hide the progress bar of Invoke-WebRequest
$oldProgressPreference = $ProgressPreference
$ProgressPreference = 'SilentlyContinue'

$desktopAppInstaller = @{
  fileName = 'Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.msixbundle'
  url      = $(Get-LatestUrl)
  hash     = $(Get-LatestHash)
}

$vcLibsUwp = @{
  fileName = 'Microsoft.VCLibs.x64.14.00.Desktop.appx'
  url      = 'https://aka.ms/Microsoft.VCLibs.x64.14.00.Desktop.appx'
  hash     = '6602159c341bafea747d0edf15669ac72df8817299fbfaa90469909e06794256'
}
$uiLibsUwp = @{
    fileName = 'Microsoft.UI.Xaml.2.7.zip'
    url = 'https://www.nuget.org/api/v2/package/Microsoft.UI.Xaml/2.7.0'
    hash = "422FD24B231E87A842C4DAEABC6A335112E0D35B86FAC91F5CE7CF327E36A591"
}

$dependencies = @($desktopAppInstaller, $vcLibsUwp, $uiLibsUwp)

foreach ($dependency in $dependencies) {
  $dependency.file = $dependency.fileName
  iwr $dependency.url -OutFile $dependency.file
}

Expand-Archive -Path $uiLibsUwp.file -DestinationPath ".\Microsoft.UI.Xaml.2.7" -Force
$uiLibsUwp.file = ".\Microsoft.UI.Xaml.2.7\tools\AppX\x64\Release\Microsoft.UI.Xaml.2.7.appx"
Add-AppxPackage -Path $desktopAppInstaller.file -DependencyPath $vcLibsUwp.file,$uiLibsUwp.File

rm $desktopAppInstaller.file
rm $vcLibsUwp.file
rm -r .\Microsoft.UI.Xaml.2.7*
Write-Host "WinGet installed!" -ForegroundColor Green
$ProgressPreference = $oldProgressPreference
Update-EnvironmentVariables
# winget install Microsoft.WindowsTerminal
# winget install ubuntu

The Microsoft.UI.Xaml.2.7.appx extraction can be more efficient, so I updated it:

$ErrorActionPreference = "Stop"
$apiLatestUrl = 'https://api.github.com/repos/microsoft/winget-cli/releases/latest'
$tempFolder = $env:TEMP

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
$WebClient = New-Object System.Net.WebClient


function Update-EnvironmentVariables {
  foreach($level in "Machine","User") {
    [Environment]::GetEnvironmentVariables($level).GetEnumerator() | % {
        # For Path variables, append the new values, if they're not already in there
        if($_.Name -match 'Path$') {
          $_.Value = ($((Get-Content "Env:$($_.Name)") + ";$($_.Value)") -split ';' | Select -unique) -join ';'
        }
        $_
    } | Set-Content -Path { "Env:$($_.Name)" }
  }
}

function Get-LatestUrl {
  ((Invoke-WebRequest $apiLatestUrl -UseBasicParsing | ConvertFrom-Json).assets | Where-Object { $_.name -match '^Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.msixbundle$' }).browser_download_url
}

function Get-LatestHash {
  $shaUrl = ((Invoke-WebRequest $apiLatestUrl -UseBasicParsing | ConvertFrom-Json).assets | Where-Object { $_.name -match '^Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.txt$' }).browser_download_url

  $shaFile = Join-Path -Path $tempFolder -ChildPath 'Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.txt'
  $WebClient.DownloadFile($shaUrl, $shaFile)

  Get-Content $shaFile
}

# Hide the progress bar of Invoke-WebRequest
$oldProgressPreference = $ProgressPreference
$ProgressPreference = 'SilentlyContinue'

$desktopAppInstaller = @{
  fileName = 'Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.msixbundle'
  url      = $(Get-LatestUrl)
  hash     = $(Get-LatestHash)
}

$vcLibsUwp = @{
  fileName = 'Microsoft.VCLibs.x64.14.00.Desktop.appx'
  url      = 'https://aka.ms/Microsoft.VCLibs.x64.14.00.Desktop.appx'
  hash     = '6602159c341bafea747d0edf15669ac72df8817299fbfaa90469909e06794256'
}
$uiLibs = @{
    nupkg = @{
        fileName = 'microsoft.ui.xaml.2.7.0.nupkg'
        url = 'https://www.nuget.org/api/v2/package/Microsoft.UI.Xaml/2.7.0'
        hash = "422FD24B231E87A842C4DAEABC6A335112E0D35B86FAC91F5CE7CF327E36A591"
    }
    uwp = @{
        fileName = 'Microsoft.UI.Xaml.2.7.appx'
    }
}
$uiLibs.uwp.file = $PWD.Path + '\' + $uiLibs.uwp.fileName
$uiLibs.uwp.zipPath = '*/x64/*/' + $uiLibs.uwp.fileName

$dependencies = @($desktopAppInstaller, $vcLibsUwp, $uiLibs.nupkg)

foreach ($dependency in $dependencies) {
  $dependency.file = $dependency.fileName
  iwr $dependency.url -OutFile $dependency.file
}

$uiLibs.nupkg.file = $PSScriptRoot + '\' + $uiLibs.nupkg.fileName
Add-Type -Assembly System.IO.Compression.FileSystem
$uiLibs.nupkg.zip = [IO.Compression.ZipFile]::OpenRead($uiLibs.nupkg.file)
$uiLibs.nupkg.zipUwp = $uiLibs.nupkg.zip.Entries | Where-Object { $_.FullName -like $uiLibs.uwp.zipPath }
[System.IO.Compression.ZipFileExtensions]::ExtractToFile($uiLibs.nupkg.zipUwp, $uiLibs.uwp.file, $true)
$uiLibs.nupkg.zip.Dispose()

Add-AppxPackage -Path $desktopAppInstaller.file -DependencyPath $vcLibsUwp.file,$uiLibs.uwp.file

rm $desktopAppInstaller.file
rm $vcLibsUwp.file
rm $uiLibs.nupkg.file
rm $uiLibs.uwp.file
Write-Host "WinGet installed!" -ForegroundColor Green
$ProgressPreference = $oldProgressPreference
Update-EnvironmentVariables
# winget install Microsoft.WindowsTerminal
# winget install ubuntu

Basically just makes sure that we only extract the necessary file, instead of extracting all the files (which aren't needed).

Just put in my last edit, in case anyone was testing and having errors.