Hi,

The normal flow in Odoo is to convert sales order into projects (using service products who are configured to create tasks). So, you first convert the Opportunity to  Quotation (via convert to quote button)  then from this Sales Order (validate button) you can create  Project and tasks. This need some configuration has to be done.

For generating the project/task from the sale order:- https://www.odoo.com/documentation/user/12.0/project/advanced/so_to_task.html

If the above flow is not preferred you can check for the addons in the odoo apps store: https://www.odoo.com/apps/modules/12.0/bi_crm_task/