The register for Order Classes is common for Sales orders and Service orders. When I set an Order Class to create an Activity - it works for Sales Order, while for Service Orders - not. Is any setting necessary to have activities from Service orders created automatically?

are the activity set as Hansamanuals said?

https://www.hansamanuals.com/main/mailnumber___62526/theconf___231/manuals/version___20250224/langcode___es/hwconvindex.htm?shortcode=HW0301SETTINGS_Order_Classes

Activity from Order
Use these options to specify whether you would like Activities to be created automatically when you save Orders belonging to the Order Class for the first time.
The Task Type of these Activities will be To Do, and the Symbol will be Other. The Start Date will be the Order Date. The Activity Type will be taken from the field below or, if that is blank, from the Activity Types, Subsystems setting in the CRM module.
The Person in the new Activities will be chosen as follows:
Use Salesman From Order
If you select this option, the Salesman in the originating Order will be copied to the Persons field in the new Activity.
Use Salesman:
Choose this option if you need the new Activities to be created in the name of a particular Person. Enter the Person's Signature in the field next to this option, using 'Paste Special' if necessary.
If an Order does not belong to an Order Class, you can still have an Activity created automatically when you save the Order for the first time. Select the Generate Activities option for Sales Orders in the Activity Types, Subsystems setting.