List v3 is disabled for related lists by default. You can enable List v3 for related lists by editing a property.
Before you begin
Role required: admin
Procedure
List v3 is no longer available for new deployments. If you are already using List v3, you can continue to do so. There are several aspects of list administration that are specific to List v3.
https://docs.servicenow.com/bundle/orlando-platform-administration/page/administer/list-v3-administr...
Difference between list v2 and v3 :-