In V13 Odoo determines the probability to close a deal with a statistical analysis based on historical information/data.

Therefore, if there is no historic data in the CRM app, the system has no information to be able to calculate/compute the probability (probability will therefore be 0%).

However, the more you add data/information in the application, the more accurate the computation of the probability will be. The computation of the probability will continuously evolve based on the information/data that is being added in the application.