Uniqlo Shirts see roughly 10 watched departures a week across the five main EU Vinted markets, with Uniqlo averaging about €18 in asking price at departure. That is real, current demand — whether an individual item is worth buying depends on its condition, size and the price you pay.
Category demand tells you people are buying. It doesn't tell you whether this item, in this size, at this price, will make you money. Three things decide that: the buy-below price (the most you can pay and still profit after fees), the sell-through rate for the specific model, and whether the size is one that actually moves.
A strong category with the wrong size is still dead stock. That is why per-size demand matters as much as brand demand.
Look up the exact model rather than the category. Resale IQ returns a BUY / WATCH / SKIP verdict with the buy-below price, typical price at departure, departure momentum and the sizes that move fastest — computed from 6,030,000+ listings across Spain, France, Germany, Italy and Portugal.
If you are new to this, the reselling manual walks through the margin maths, the fee structure and the sourcing rules that decide whether a category like this is actually worth your money.