As of Visual Studio 2019, the original feature to create Test Certificates have been removed in order to, "promote better security practices". A bug report has been filed, but it does not seem that this feature will be coming back soon.

Taken from Pengwin Build Instructions

ISSUE SEEM TO BE FIXED BY NOW but this short powershell snippet to generate own test cert without using VS can be still quite handy:

$Subject = "CN=Your-appxmanifest-publisher"
$Store = "Cert:\CurrentUser\My"

# Delete old certificate
Get-ChildItem $Store | Where-Object { $_.Subject -match $Subject } | Remove-Item

# Create new certificate
New-SelfSignedCertificate -Type Custom -Subject $Subject -KeyUsage DigitalSignature -FriendlyName "Pengwin Test Certificate" -CertStoreLocation $Store -TextExtension @("{text}", "{text}")