Ehh depends on the country, personally in Spain I reported my gains in crypto last year and they were quite ''generous'' to overlook a lot of transactions and other evidence that I didn't have. In fact I almost only needed to provide the exchanges trades and a few screenshots here and there since bitcoin is still not fully regulated here. Problem is that if you keep evading taxes they will bite you in the ass one day, specially if you are planning to make a substantial amount of money through cryptos, you will eventually want to buy a house a car, etc, how are you going to do it?