You put money into a Roth IRA through the backdoor when you aren’t eligible to contribute to it directly. You pay tax on a small amount of earnings if you waited between contributions and conversion. That’s negligible relative to the benefit of having tax-free growth on your contributions...
Taxes are due when you sell, trade or dispose of your cryptocurrency investments in any way that causes you to recognize a gain in your taxable accounts. This doesn’t apply if you trade cryptocurrency in a tax-deferred or tax-free account like an individual retirement account ...