Core Modules are features that ship with the core Jetpack CRM plugin that can be enabled or disabled according to your needs. For example, you may not need the Quotes or Invoices. There is an option to disable those modules from your dashboard. Here’s how to do that:
First of all, from your wp-admin dashboard, click Jetpack CRM > Core Modules. You’ll see a page like this:
You can hover your cursor over any of the modules that you want to activate or deactivate and you will find the button to do so. In the screenshot above, the Invoices module is active. By hovering the cursor over the Invoices module, we see the option to deactivate it.

From the Core Modules section, you can deactivate any functionality from your site if you don’t need it.
More on Core Modules:
Using the WooCommerce Sync Hub
How does the Client Portal Work?