macOS High Sierra requires you to explicitly allow a newly installed 3rd party system extension. To complete the installation of Yam Display, please allow loading the extension in System Preferences > Security & Privacy > General and restart your Mac.
There are known issues of macOS High Sierra that require more Mac resources than the previous macOS.
Please reduce the frame rate or resolution for laggy cases.
We expect the issues will be resolved as macOS High Sierra becomes stable.