The difference here is that for leftists, liberalism is still evil, just that fascism is far more so. Biden would still be considered the lesser of two evils in that instance.

Talking down to leftists as though their complaints are illegitimate and pushing a narrative that "Biden is good, actually" just furthers voter apathy, the correct way to engage with leftists is to point out how voting as a leftist is loss prevention. Because voting will never move America to the left, leftists must work on the ground to build grassroots movements, unionize, organize, protest, and more, while voting Democrat to keep fascists out of office.

Telling clearly passionate people that their criticisms are invalid and that their problems don't matter is an extremely privledged position to hold. For many people, the status quo itself is bad. People can't afford to just vote Democrat, they already can't afford many necessities and are already being targeted by fascists.