I do not understand what you meant by instant exchanges as all cryptocurrency exchanges are instant. If you want to find about non KYC exchanges, that I think you are asking then visit this website - https://kycnot.me/

They have a list of non kyc exchanges where you can trade without waiting for KYC approval. Those listed are legitimate but ensure you do your own research before investing your money or doing any trade.

The reason being non kyc exchanges cannot be trusted.