Elements: Smart Object support in mockup use

Hey, I'm trying to test PE in use as mockup tool. I bought a lot of mockup files to put my designs into, but looks like using of Smart Objects doesn't work as in regular Photoshop.
Also, on tutorials on YT, they use "paste into selection" command but I have it inactive all the time I work on Smart Object.
Is it possible to work with such elements at all? :)