How to provide tenant admin permission to app only provider hosted add-in on SharePoint 2019 On-premise

I used this script to make a site collection tenant admin in SharePoint 2019 on-premise.

After that I was able to give my app tenant scoped permissions by navigating to the "/_layouts/15/appinv.aspx" relative to the url of the tenant admin site collection.

# Enable the remote site collection creation for on-prem in web application level
# If this is not done, unknon object exception is raised by the CSOM code
$snapin = Get-PSSnapin | Where-Object {$_.Name -eq 'Microsoft.SharePoint.Powershell'}
if ($snapin -eq $null) 
{
    Write-Host "Loading SharePoint Powershell Snapin"
    Add-PSSnapin "Microsoft.SharePoint.Powershell"
}    
$webapp = Get-SPWebApplication $webAppUrl
$webapp.SelfServiceSiteCreationEnabled = $true
$webapp.ShowStartASiteMenuItem = $false
$newProxyLibrary = New-Object "Microsoft.SharePoint.Administration.SPClientCallableProxyLibrary"
$newProxyLibrary.AssemblyName = "Microsoft.Online.SharePoint.Dedicated.TenantAdmin.ServerStub, Version=16.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c"
$newProxyLibrary.SupportAppAuthentication = $true
$webapp.ClientCallableSettings.ProxyLibraries.Add($newProxyLibrary)
$webapp.Update()
Write-Host "Successfully added TenantAdmin ServerStub to ClientCallableProxyLibrary."
# Reset the memory of the web application
Write-Host "IISReset..."    
Restart-Service W3SVC,WAS -force
Write-Host "IISReset complete on this server, remember other servers in farm as well."
# Set admin site type property to the site collection using PS for any site collection type.
# This is needed to be set for the site collection which is used as the 
# "Connection point" for the CSOM when site collections are created in on-prem
$site = Get-SPSite -Identity $siteColUrl
$site.AdministrationSiteType = [Microsoft.SharePoint.SPAdministrationSiteType]::TenantAdministrationeType = [Microsoft.SharePoint.SPAdministrationSiteType]::TenantAdministration