I think this question should be rephrased: what if governments declare all cryptocurrencies illegal?

Because it would make no sense to ban just one, be it btc or another, people would just switch to a different crypto and the govt would not achieve much considering their care is not for people losing their money or homes due to mindless all-in trading, but their only care being to keep collecting taxes so that our chosen few may live lives of luxury off our hard earned money, and the real leaders of this world and owners of most assets on the planet, banks, will maintain control over all money supply and currency transfers.

So...what will happen if orning or buying or selling crypto becomes illegal? Like, jail time illegal. As in, every possible buyer or seller could be an undercover agent working for whatever govt agency will enforce the ban.