BACKGROUND: Loneliness and depression in older people are increasing worldwide. Proficient nursing practice requires the continuous and long-term development of clinical knowledge. Lifelong learning is essential and enhances clinical nursing practice. Nursing includes various functional areas that illustrate registered nurses' wide range of responsibilities to ensure healthcare quality. Registered nurses are committed to working comprehensively, observing patients and identifying symptoms of both physical and mental ill-being. The aim of this study is to explore how registered nurses perceive their clinical competence in observing signs of loneliness and depression in older people in home care, and which barriers in home care services prevent quality improvement. METHODS: Fifteen registered nurses from home care units in Norway were individually interviewed, and the interviews were analysed using qualitative content analysis. RESULTS: The analysis revealed three themes in accordance with the study aim: I) Uncertainty about knowledge of mental health, II) Lack of opportunities to meet the patients' needs regarding mental ill-being, III) Feelings of guilt for not doing enough for patients. CONCLUSIONS: Lack of education and training in mental health creates uncertainty and limits registered nurses' ability to effectively address signs of loneliness and depression. Registered nurses often feel unprepared to handle psychological aspects of care. Organizational barriers hinder effective care. Additionally, the emotional toll on registered nurses, who experience guilt and moral distress due to their limited ability to provide sufficient care, highlights the impact of these systemic issues on patients. The study underscores the need for improved training, better collaboration, and stronger leadership to prioritize mental health and ensure that registered nurses have the necessary resources and support to meet the needs of older people with signs of mental ill-being in home care.