The US and UK are reviewing more than $20 billion of cryptocurrency transactions that passed through a Russia-based virtual exchange, according to people familiar with the matter, as part of allied efforts to crack down on the sanctions evasion that’s supporting Vladimir Putin’s war in Ukraine.The payments under scrutiny went through Moscow-based crypto exchange Garantex using the dollar-pegged cryptocurrency Tether, the people said, speaking on the condition of anonymity to discuss a matter tha...