Is it possible to prevent calling line identification on an incoming call?

Only for external VoIP accounts or on an analogue terminal. On external ISDN connections, to ISDN or VoIP extensions, caller identification cannot be prevented.
In the configuration of the VoIP provider used, a user-defined evaluation can be defined under Evaluation of incoming SIP messages, in which all selections for search prioritization are set to None.
For analog terminals, the CLIP info can be deactivated under Subscriber / Function overview / Analogue settings.