Why is it that when I create a communication site or team site in Modern UI they are not listed in the SharePoint admin as site collection?
Thanks in advance
This is a known issue. It will not appear in the "classic" admin center. It will show up in the new "Modern (new and improved)" admin center which will be released later this year.
The only way to get it is using PowerShell as of now.
PS command in SharePoint online -
Get-SPOSite -Template SITEPAGEPUBLISHING#0
Youtube link - New admin controls for SharePoint and OneDrive for Business