We are planning to migrate to 2019 from 2013 and we are in planning phase and we trying to find the list of unsupported templates not the decprecated ones.
as far as i know their is no removed template from SharePoint 2016 / 2019. Rather they add the new templates related to compliance center etc.
But their are some obsolete templates in SharePoint 2019, you can get the list by running this command
Get-SPWebTemplate | select name, title,description
it will list of all templates and look for the "Obsolete",
SPS#0 SharePoint Portal Server Site This template is obsolete.
You can check the list of all templates here: https://social.technet.microsoft.com/wiki/contents/articles/52674.sharepoint-server-2019-list-of-all-templates.aspx
You can retrieve list templates using the following PowerShell:
$SPWeb = Get-SPWeb "http://URLtotheSite" $SPWeb.ListTemplates | Select Name, type, type_client, Description $SPWeb.dispose()
Note:change the "http://URLtotheSite" to your site URL.