If after installing the ON1 plug-ins are are not showing in Photoshop CC 2019, the first thing we would recommend would be to re-run the installer.
You can download and install over what is currently installed from this link:
If you are still not seeing the plugins in Photoshop, you can copy and paste the plugin files which are located in the Applications/ ON1 PHOTO RAW 2019/ Plugins folder. In here there are folders containing each plugin. (go into each folder here and copy the plugin file)
You want the Develop, Effects, Portrait & Resize plugins that end in .plugin file extension.
You do not want to copy the Resize lrplugin or ON1 PHOTO RAW 2019.lrplugin files.
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)