Check if an application is installed

[string]$appDisplayName = 'App Volumes Agent'

if( ( Get-ItemProperty 'HKLM:\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*' -Name DisplayName -ErrorAction SilentlyContinue | Where-Object DisplayName -match $appDisplayName ) `
    -or ( Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*' -Name DisplayName -ErrorAction SilentlyContinue | Where-Object DisplayName -match $appDisplayName ) )
{
    "`"$appDisplayName`" is installed"
}