I’m a Long Covid sufferer since Spring 2020 with persistent lack of smell…I can largely identify the basic sweet, salty etc etc tastes but hardly any flavours, relying on textures. It has certainly changed my diet, and affected the pleasure I used to get from cooking, socialising and going out for a meal. About 2 years ago I started forcing myself to eat to get nutrients consumed, weirdly before though eating about third of what I used to eat pre covid I did not loose weight. I know of researchers who are looking into the link between such limited diets, poor gut biome and mental health, specifically anhedonism( opposite of hedonism ie lack of joy from the senses) and depression. Dr Monty Lyman a UK research psychiatrist is currently looking at this; he has also written numerous popular books, very readable and well referenced, linking the physiological and mental aspects of numerous ‘processes’ like pain and immunology, but don’t think he has published anything re. anhedonism yet. My son, also a UK psychiatrist, is very keen on exploring a patient’s eating habits, mineral and vitamin levels too…has your brother been blood tested for the ‘basics’ vit D, B12, ferritin and folate, or any others? What were the results? You might find the website Zoe Nutrition interesting: lots of genuine research, podcasts etc re.a whole range of poor health linked to bad ( or little) diets and poor gut biome and tips how to improve it…eg remove ultra processed food, add fermented foods like plain yoghurt, and 30 different plant foods a week…definitely worth a try. I’ve adopted them, and despite LC, of which my worst symptoms are very disabilitating faints from sudden low BP on standing, have remained comparatively content! If you want more nutritional tips, I’d be glad to help with suggestions.