We have had similar threads before.
In my experience what meals are called and when they are eaten depends on the following factors:
where and when you were born, and what the mealconsisted of and when it was eaten.
My grandparents who grew up in Edinburgh and spent most of their working lives in Bradford ate their main meal at middday and called it dinner. They had tea after Grandpa came home from work at night.
This was common practice amongst their generation in Scotland and a great deal of the north of England.
My parents' generation ate lunch - quick, cooked meal, in the middle of the day. It's main function was a stop-gap between breakfast and dinner, eaten about 6 p.m. Some families still ate dinner at midday, but most men did not come home from work during a dinner-break at midday, so the main meal tended to be eaten in the evening.
My Danish relatives who lived in Copenhagen, ate a cold lunch either at home or at work /school in the middle of the day, and a cooked dinner at night. Those who lived in the country still ate dinner at midday, and a cold meal in the evening.
I have heard the word "supper" as a child, but only used in other regions of the UK to where we lived. In the Glasgow area, some families had afternoon tea - mainly something enjoyed by ladies visiting friends in the afternoon, and some called their evening meal High Tea, where a cooked dish was eaten. It resembled lunch as far as the cooked, often fried food went, but tea was drunk at it, which was not usual at lunch.