If for some reason your plugins are not appearing in Photoshop after installation you can manually move or copy/paste them from the following location:
Goto the Applications folder/ ON1 PHOTO RAW 2020/ Plugins folder. In here there are folders containing each plugin. (go into each folder here and copy the plugin file)
You want to copy the Develop, Effects, Portrait & Resize plugins that end in .plugin file extension.
*NOTE: You do not want to copy the Resize lrplugin or ON1 PHOTO RAW 2020.lrplugin files. These are for Lightroom ONLY.
You can copy and paste (or move these files) to the following location:
MacHD>Library>Application Support>Adobe>Plugins>CC: (Paste Plugins into this folder)