It’s a frigging figure of speech. It doesn’t literally mean both options are “evil” anytime it is used. And you’re not “choosing evil” by voting for Biden — not for the people whose lives will be ruined if Trump wins. For many you are preventing evil.
If a few more people in a few states had chosen the “lesser evil” of Hillary over Trump, the Supreme Court wouldn’t be delivering supreme evil every few months for the foreseeable future.
(I don’t need to hear about how Hillary did a bad job in the election — it doesn’t change the fact that the consequences are what they are.)