Some of our installers are 32-bit applications, and since macOS Catalina, 32-bit apps are not supported.
They will eventually all be updated to be 64-bit installers*, but until then you will have to find and use the red “Install Product” button in the Product Manager application to install the product that you are trying to install.
Toontrack Product Manager allows you to install the software even though the installer you downloaded is a 32-bit application.
* Not the discontinued product installers.