Hi there,
yes templates should appear in the library panel but not necessarily in the library called 'My Library'
When you download a template it appears with a blue check mark

You know it has been saved to your hard disk because it shows up under the 'saved' tab

If you want you can open it from there

If you look at Libraries on the Adobe website you see all your current libraries. In the top right corner of the libraries panel select 'view on website'

A browser will open. As you can see Stock Templates have a dedicated folder and don't go into the default 'My Library'.

This can sometimes be a problem and you may have to 'Create a new library yourself. In the library panel called 'Stock Templates'

It happened automatically for me, but I'm using Windows so a Mac maybe more obstinate. However you only need to do this once
After that your templates should be visible in the library like below.

Templates are just Psd files with a Psdt extension. In fact you can create your own template from a psd file by renaming it *.psdt. You can find them on your hard disk by doing a search on *.psdt, but Adobe have not been particularly helpful as they reside in hidden folders with GUID names and so you need to make those folders visible before you can see them. On Windows it's just a matter of making changes in folder options, but I think it's a little more involved on a Mac.
To speed up a search on Windows jump to the 'AppData' section. Like below
C:\Users\<profileName>\AppData\Roaming\Adobe\
The Mac folders are arranged differently so one of our Mac users would need to tell you the precise location there.