in my mind voting in our current system is just pretty straightforward utilitarian calculus (and can't be anything else): you should vote for the option which will do the least harm and has the highest probability of winning. even if you, say, accept that Biden and Trump are equal on I/P, that just means you should look to other issues on which they are distinct--and they are distinct on basically every other issue in a way that clearly suggests Biden to be the best choice you can make here.
take just the Autocracy Tracker, which makes it unambiguous that Trump, if he wins, is planning a sweeping authoritarian wave of deportations, purges, restrictions of civil rights, and repression of minority groups and ideological groups he disagrees with. much of this is, in a sense, already happening here and already a form of genocide against some groups (trans people most prominently--it is now de facto illegal to be trans and legal to bring harm to trans people in large portions of the US). a Trump win will probably ensure there is no safe place for such groups in this country anymore.
on a moral level: i am just not sympathetic to the idea that voting for Biden constitutes blood on your hands in a meaningful way. i think if you accept this line of argumentation, you would ultimately have to bite the bullet that this could also be said of paying taxes[^1]--and i certainly don't begrudge people for paying their taxes even as this lines the pocket of the war machine, so then why should judge them for voting? in general: by virtue of existing within a state, you will always be complicit to some degree in the crimes of that state, regardless of what you do to extricate yourself from supporting them. so i just don't think that abstention from voting or voting for a more morally defensible alternative actually cleans your hands of the blood being perceived here.
separately, and more pragmatically: there is no compelling third party with anywhere near a possibility of winning or even scoring a "symbolic victory." a vote for a leftist third party right now is, in a real sense, a vote wasted--because these parties are incompetent, fractured, and full of people who are not serious candidates. even with the Green Party (by far the most electorally advanced of them) nobody has ever trembled at their influence and in practice they mostly seem to exist to waste a lot of the money given to them on quixotic presidential candidates. imo: any actual movement challenging the power--your DSAs, for example--is going to be built from the ground up and not imposed through the presidency, and is only going to use electoralism as one of its several political arms.
[^1]: arguably, it's even more true of paying taxes than of voting: votes may make no difference in whether something happens or not, but taxes actively make them possible
you may take the United Fruit Company's name, but you can't take its legacy of financing terrorism and violence in Latin America...