When the Piapro Studio isn’t dislpayed as a AU plug-in, the version of your Piapro Studio may not be adjust for AU.

Update to the latest version manually and check again.
Check this out for the way to update.

Depens on the DAW software, you need to scan the plug-in.

When it isn’t displayed even though you update to the latest version, try the rescan of the plug-in in your DAW software.
*For the way to scan the plug-in, Check manual or product company of your DAW software.