I'm not sure how well this will go as a thread, these kind of threads usually bring out the competitive under and over eaters and exponents of quite extreme diets which is not particularly helpful in trying to work out what is 'average' or 'normal'. The internet generally (and MN no different) is full of people who are very loud and confident about their own particular version of what is 'normal' and 'healthy' and insistent only their version is the truth, whereas in science and the real world there's a huge amount of variation both in terms of what is 'good' and 'healthy' for one person but also what can be empirically proven to be a positive in terms of an overall diet, once you control for other factors like individual circumstances and preferences, cultural and generic differences etc. As although on a micro level science can show that a certain vitamin or mineral is valuable for particular bodily functions, it's very hard to proof with proper large scale randomised controlled trials what is 'best' as a whole diet, as you simply can't control closely enough what people eat over a long enough period with enough participants to be really certain of your conclusions. So we're left with quite a lot of doubt and uncertainly which is obviously difficult to then know what you should do as an individual.
But to answer your question, overall I feel the things which have consistently been shown to be generally healthy but also achievable by an average human living in the UK are along the lines of the much-maligned NHS eat well guide and/or the planetery health diet and/or the mediterranean diet. I.e. a diet which is based largely on lots and lots of fruit, veg, pulses, grains and legumes, moderate portions of wholegrain carbohydrate, lean protein and fats, nothing forbidden but alcohol, highly processed food and sweet 'treats' only in moderation. I would not say I mange to stick to this aspiration 100% perfectly, not at all, but a typical week for me (I think it's much more helpful to think in terms of a weekly or monthly average than a daily basis as a busy weekday would look very different to a lazy weekend for instance) involves no breakfasts (I've never been a big breakfast eater), light lunches of soups, salads, leftover dinners, and largely home cooked dinners of typical family things like curry, chilli, stir fry, stews, pasta - with some more convenience foods thrown in as needed. I am veggie so my protein is usually lentils, chickpeas, tofu, beans etc., but DH largely has fish or chicken with red meat maybe once a week. Fruit and yoghurt or cheese as desserts/snacks (I try to avoid snacking between meals as a general rule but if I must it's one of these). Alcohol and chocolate/cake/crisps/biscuits only at the weekends unless a special occasion. Usually a takeaway or a meal out sometime at the weekend too.
In terms of the psychology of it, the best tip someone ever gave me was to always think in positive terms of what you can 'start' doing or 'add in' to your existing diet and lifestyle, rather than what to 'stop', 'cut out', 'forbid' etc. Personally as soon as something is 'not allowed' I (a) immediately want that thing much more and (b) if I have the thing, will tend to consume to excess as once the rule is broken it seems pointless to stop. So I think about what things I should do, i.e. eat 5 a day, plan and cook tasty homemade meals, drink plenty of water, make time to exercise, take care of myself well mentally, build in destress/relaxation points in the day (that don't involve food!) and focus my energy on doing those things first as well as rather than stopping the 'bad' or less healthy habits. It's a bit un-inuitive to think about eating more rather than less, particularly if you are aiming to lose weight or body fat but if you've had 1-3 delicious healthy meals with plenty of fruit veg and good nutrients, you'll naturally be less hungry for junky food anyway. But the point is even if you do still end up having the treat, that doesn't negate the benefits physically and mentally of the other good food you've had that day. And you don't then need to gorge yourself on the treaty food, you can have it again tomorrow if you still want it. I tend to find if I put the proposition to myself that way, quite often I don't want the treaty thing as much as I thought I did, or I can manage having just a smaller portion and save the rest for tomorrow. I've probably explained that badly but I follow a guy on social media called Ben Carpenter who is really good on explaining this stuff, he's a personal trainer by background but unlike many PTs (sorry PTs in general!) he's really really hot on the science but also explaining things in an accessible and realistic way, understanding that food is a complex and emotive subject for many of us and that we all live in the real world not some 'influencer's' fantasy where protein smoothies and steak 3 times a day is totally realistic. I'd really recommend his videos...