$Home is a Powershell “automatic variable”, see all the variables with:
get-help about_Automatic_Variables
your code should work like this:
$HomePage = .(Join-Path $PSScriptRoot "pages\home.ps1")
$Onboarding = .(Join-Path $PSScriptRoot "pages\onboarding.ps1")
Start-UDDashboard -Wait -Dashboard(
New-UDDashboard -Title "New Dashboard" -Pages @(
$HomePage,
$Onboarding
)
)