The only folders there are, CC, CS6, and Elements 9, 11, 13, 14, and 15.
Here’s where my PE 16 Plug-ins folder is: User library > Containers > com.adobe.pse.16editor > Data > Library > Application Support > Adobe > Adobe Photoshop Elements 16 Editor > Plug-ins > TopazDeNoise6 > TopazDeNoise6.plugin.
But when I open PE 2018 Editor, open a photo, and select Topaz Labs - Topaz DeNoise 6, I get this, "Cannot Proceed - Error: please report this error to Topaz Labs".
I don't have access to any adobe applications from the mac app store, so maybe a another user or an adobe employee knows, but i've heard one can't install actually plugins or updates unless apple provides them thru the app store.
Anyway, if you have a previous version of photoshop elements installed and in the 2018 version under Adobe Photoshop Elements Editor>Preferences>Plugins has a check for an Additional Plugins Folder, you could point it at a previous version of elements plugin folder as shown below.
Then restart pse 2018 for the setting to take affect.