Topic: Pianoteq Stage in Sibelius Ultimate (Mac)

Sibelius no longer recognizes Pianoteq Stage as a plugin. There is no button titled "Folder" under Play / Mixer / Audio Engine Options. I'm told this is where to look:

Library / Application Support / Avid / Sibelius / Plugins

But there is no Pianoteq file there and I don't know what to add.

macOS 10.14.4
Sibelius Ultimate