Many funding programs, especially public funding agencies, now require that the results of the research they fund be made available in repositories. This is to ensure that the results of the research they fund are easily accessible and usable by the public and the scientific community. In addition, clearly defined data management in the form of a data management plan (DMP) is increasingly required with the project proposal and is taken into account when evaluating research projects.
Horizon Europe stands for Open Science by default from the application phase to project reporting. In the area of research data, the FAIR principles always apply - "As open as posible. as closed as necessary".