Some products of CorelDRAW will not include the “Automation support”. This feature is required to be able to install the Summa plugin.
When the “Automation support” feature is not available in the CorelDraw than the Summa plugin cannot be installed.
For example CorelDRAW Essentials 2020, CORELDRAW Standard 2020 do not support this “Automation support” feature and the plugin will not work in those versions of CorelDRAW.
Below you see a printscreen of the CorelDRAW website. There it states under the "Key Features & Tools (Highlights)" that "Automation support (VSTA, VBA), Macro Manager" is only available in the CorelDRAW Graphics Suite 2020.
Please check the CorelDraw website to verify if your CorelDRAW Product does support this key feature.