The third edition of this series of Workshops was held in Burgos from October 2 to October 6, 2023, and brought together experts in Quantum Foundations, Quantum Information Theory, Quantum Gravity, and Philosophy of Physics, fostering open discussions on various aspects of the notion of observer. The aim of the present edition was to continue our exploration of recent developments in this rapidly evolving field.  This Workshop provided a dynamic discussion forum, with a specific emphasis on applications and connections with Quantum Communication Protocols and Systems.