That's a practical question that touches on urban design and everyday safety. Generally, most standard public or municipal trash bin lids are not designed or tested for someone to sit on them. Their primary function is to cover waste.
Typically, these lids are made from durable plastics like HDPE or metals and are built to withstand weather, occasional impacts, and the weight of typical debris. An informal estimate might put their static weight capacity in the range of 25-50 kg (55-110 lbs) before risk of cracking or the hinges failing. However, this is highly variable. Factors like material quality, age, sun exposure (which weakens plastic), and the design of the hinges and bin frame are crucial.
It's important to note that sitting on a bin lid is not recommended. Manufacturers do not rate them for this purpose, so there is no official "weight capacity" for sitting. The action poses several risks: personal injury from the lid breaking or the bin tipping over, potential damage to public property, and hygiene concerns.
For actual seating in urban spaces, look for benches or seating elements specifically engineered and rated for human weight, which often support over 135 kg (300 lbs). If you're curious about a specific bin's strength, the safest answer is to avoid testing it yourself and treat public infrastructure with care.