I use the onion site again and wanted to use it to exchange bitcoin for bitcoin and I saw that you are right. The site would be said to be a mixer because of that. An exchange should be a platform that one coin can be exchanged to another and not the same coin. If it is the same coin it is a mixer.
You can expand this to bridges that allow users to bridge from one cryptocurrency to another cryptocurrency.
So if the expansion is right in the concept, will cryptocurrency bridges, from one blockchain to another, from layer 1 to layer 2, will soon be classified as mixers in future.
I am very curious that will bridges become next targets of SEC. and DOJI.