Not sure where you are, but here in the UK there is a large range of garden sizes, and generally urban areas have smaller gardens. During the industrial boom, houses were packed into small plots as they were designed to be functional, worker's accomodation. As a result local councils were obliged to free up communal areas for households to have a growing space. This developed into what we now call allotments because each house was alloted a measure of land. The plots were 10 rods in size, roughly 250 sqm.
The plots are rented and you hold your plot as long as you want but cannot pass it to your heirs. You also cannot grow commercially. Most plots have rules about what structures you can have or livestock you can keep. A lot of people keep chickens or bees on allotments.
I used to have an allotment when I lived in a small Victorian cottage but gave it up when I bought my current house which has a large garden and allows me to grow a decent amount of my own produce.
I love watching the veggie youtubers but have some favourites from other countries aswell.