A workaround for "node-gyp is unable to find msbuild if VS2019 is installed": https://github.com/nodejs/node-gyp/issues/1663

make-msbuild-shim.ps1

<#
This is a workaround for "node-gyp is unable to find msbuild if VS2019 is installed"
  https://github.com/nodejs/node-gyp/issues/1663
It create a shim EXE as "MSBuild\15.0\Bin\MSBuild.exe" to target "MSBuild\Current\Bin\MSBuild.exe"
By noseratio - MIT license - use at your own risk!
It requires admin mode, I use wsudo/wsudox (https://chocolatey.org/packages/wsudo) for that:
  wsudo powershell -f make-msbuild-shim.ps1 
#>

#Requires -RunAsAdministrator 
#Requires -Version 5.1
$ErrorActionPreference = "Stop"

$vsBasePath = . "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe" `
  -latest `
  -requires Microsoft.Component.MSBuild `
  -property installationPath -format value

if (!$vsBasePath) { 
  throw "VS2017+ must be installed" 
}

$msbuildSimPath = [System.IO.Path]::Combine($vsBasePath, "MSBuild\15.0\Bin\MSBuild.exe")
if ([System.IO.File]::Exists($msbuildSimPath)) {
  Write-Host "Already exists: $msbuildSimPath"
  exit 0;
}

# Create the shim .EXE using C#
$code = @"
  using System;
  using System.Diagnostics;
  using System.IO;
  using System.Linq;

  static class MSBuildShim
  {
    static void Main()
    {
      var thisExe = Process.GetCurrentProcess().MainModule.FileName;
      var thisExeDir = Path.GetDirectoryName(thisExe);
      var newExe = Path.GetFullPath(Path.Combine(thisExeDir, "..\\..\\Current\\Bin", "MSBuild.exe"));
      if (!File.Exists(newExe))
        throw new FileNotFoundException(newExe);

      var process = new Process();
      process.StartInfo.FileName = newExe;
      process.StartInfo.Arguments = String.Join("\u0020", Environment.GetCommandLineArgs().Skip(1));
      process.StartInfo.UseShellExecute = false;
      if (!process.Start())
        throw new InvalidOperationException(newExe);

      process.WaitForExit();
      Environment.ExitCode = process.ExitCode;
    }
  }
"@

Add-Type -TypeDefinition $code `
  -OutputType ConsoleApplication `
  -OutputAssembly "$msbuildSimPath" `
  -ReferencedAssemblies "System.Core.dll"

Write-Host "Shim created at: $msbuildSimPath"

Cannot process the "#requires" statement at line 10 because it is not in the correct format.

@bipolarmorgan, on the machine where you're getting this error, can you go to the admin command prompt and run powershell get-host

What is the output?

C:\Users\User>powershell
Windows PowerShell
Copyright (C) 2009 Microsoft Corporation. All rights reserved.

PS C:\Users\User> get-host


Name             : ConsoleHost
Version          : 2.0
InstanceId       : 92b8f577-b391-4aa6-aae5-8cb6beb4cf45
UI               : System.Management.Automation.Internal.Host.InternalHostUserInterface
CurrentCulture   : en-US
CurrentUICulture : en-US
PrivateData      : Microsoft.PowerShell.ConsoleHost+ConsoleColorProxy
IsRunspacePushed : False
Runspace         : System.Management.Automation.Runspaces.LocalRunspace

Name : ConsoleHost
Version : 2.0

@bipolarmorgan, so this is Windows 7 with PowerShell 2.0 and that's why you're seeing this error. You need PowerShell 5.1, as you could tell from #Requires -Version 5.1. You can get it here: https://chocolatey.org/packages/powershell.
Better yet, use the new node-gyp 5.0 and never mind this gist, it was meant to be a workaround until node-gyp properly supports VS2019.
That said, I'm not sure VS2019 is even supported on Windows 7, as the latter reaches its End of Life phase on January 14, 2020.