Script for testing installed .NET framework version, based on https://docs.microsoft.com/en-us/dotnet/framework/migration-guide/how-to-determine-which-versions-are-installed#query-the-registry-using-code

Get-lnstalledVersions.ps1

Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -Recurse | Get-ItemProperty -Name version -EA 0 | Where { $_.PSChildName -Match '^(?!S)\p{L}'} | Select PSChildName, version

Get-NetFrameworkVersion.ps1

$release = (Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full").Release
switch ($release) {
    { $_ -ge 528040 } { "4.8"; Break }
    { $_ -ge 461808 } { "4.7.2"; Break }
    { $_ -ge 461308 } { "4.7.1"; Break }
    { $_ -ge 460798 } { "4.7"; Break }
    { $_ -ge 394802 } { "4.6.2"; Break }
    { $_ -ge 394254 } { "4.6.1"; Break }
    { $_ -ge 393295 } { "4.6" ; Break }
    { $_ -ge 379893 } { "4.5.2"; Break }
    { $_ -ge 378675 } { "4.5.1"; Break }
    { $_ -ge 378389 } { "4.5" ; Break }
    Default { "No 4.5 or later version detected $_" }
}