I tried to do some research but I couldn’t find any definitive answer to this: Does the ESA initiate the development of necessary new technologies if it is necessary? And does the ESA create new space missions?
Yes, the European Space Agency (ESA) does design new mission concepts and initiates technology development activities in parallel to support the realisation of those missions.
ESA is divided into several different directorates focused on different applications. For instance, there are dedicated directorates dedicated to Human and Robotic Exploration, Science, Earth Observation, Navigation, Telecommunications, Launch and In-Orbit Transportation etc. There are typically teams within each directorate which focus on the development of future concepts and the definition of technology requirements.
ESA performs in-house mission design studies in it’s dedicated Concurrent Design Facility (CDF). In a typical early phase CDF study teams will explore the feasibility of new mission concepts and identify enabling technologies. Often the study reports from CDF studies are available to the public.
You can find a list of recent CDF studies completed here.