Is currency trading lawful? I mean like if I buy any currency e.g 1$ and when its value increases can sell it take money which is more than its old value? and it’s it lawful to buy and purchase digital currencies like crypto, bitcoin, etc…? Please explain details.

Trading in currencies is permissible, such as buying the dollar at a price, then selling it at a higher price, and so on.
Likewise, it is permissible to sell it for the same at a higher price with the sale being present, such as selling a note of one hundred dollars, for ten bills of the same ten, and five more than it, so the value is 105, provided that the sale is not deferred for a term.
As for electronic currencies, His Eminence Sayed Sistani does not allow dealing with them at the present time, as an obligatory precaution.