What is the time complexity of removing from a queue?

The time complexity of the dequeue (removal from a queue) operation is O(1).

This is because the element is always removed from the front of the queue, and this does not require traversing the whole list: it is enough to just move a pointer (or take the first element, if the queue is implemented as a linked list or a circular buffer).

Exception: if the queue is implemented on a plain array without a circular structure and elements are physically shifted on removal, then the complexity becomes O(n). That is why circular buffers or linked lists are used in practice to keep O(1).