Backward compatibility is one of USB's defining features. A new USB4 laptop can still use an old USB 2.0 flash drive, and an old USB 2.0 computer can still use a modern USB-C cable, because each generation of USB has been designed to keep working with earlier ones rather than starting from scratch.
The tradeoff is that a connection only runs as fast as its slowest link. If a modern USB4 port is connected through an old USB 2.0 cable, or to an older USB 2.0 device, the whole connection drops to that older, slower speed, even though the port itself is capable of far more. The same applies to power: an older cable may not support the higher current needed for fast charging.
This is why two setups that look identical from the outside, such as two USB-C cables, can perform very differently in practice, and why checking cable and device specifications matters as much as checking the port. See USB speeds explained for how the different generations line up.
