There is no legitimate problem in dealing with Bitcoin and similar digital currencies by buying and selling, as is the case with the rest of the currencies, goods and stocks.
The problem with digital currencies is that they do not have an external reality, but are a virtual commodity, and from this point of view, His Eminence Al-Sistani is reserved in dealing with them, and does not say that the transaction is forbidden.
And since he does not express an opinion about it, his imitators can refer to another jurist who issues a fatwa on the permissibility of dealing with it.