There are a lot of SmartThings provided ‘template’ SmartApps, but you can’t find them in the new SmartThings Connect app, nor are a lot of them shown in the old SmartThings Classic app either.
To access SmartThings home grown SmartApps, log into the ‘SmartThings Groovy IDE’ on the web, then select ‘SmartApps’ under ‘Developer Tools’. Now hit the ‘New Smartapp’ button, then select ‘From Template’ and you’ll see a lot of SmartThings home grown SmartApps.
One of them is called ‘Left it Open’ which is what I’m using for various doors. It only has a notification action so there’s no other action it can do. You just select ‘Create’ and then ‘Publish for me’ and then you’ll see it available in the SmartThings app SmartApps area under ‘My SmartApps’.