Voting third party in a plurality election dominated by two major parties is literally throwing away your vote. It's unfortunate, but true, and is why plurality voting is so, so stupid. Short of a massive event that results in the dissolution of the Democrats or Republicans and allows either the Green or Libertarians to fill the void (or actual election system reform to a competent system), the Democrats and the Republicans will always be the 2 major parties in charge. Events that unseat a major party out of 2 party dominance are exceedingly rare in plurality systems once 2 major parties cement their power.

The options are:

a) Vote for one of the two major parties currently in power, even if you hate both for varying reasons. On the plus side you at least get to vote for the lesser of two evils, but on the downside you're forced to vote for the lesser of two evils.

b) Vote honestly for your preferred candidate, even if they're a third party candidate. This hurts your ability to make a decision about the parties in charge since your vote won't have a real impact on the election outcome unless the third party happens to be close enough in votes to threaten one other party (in which case they're likely a spoiler party).

c) Officially reject your ballot. Some places allow you to record this, many do not or will record it as "did not vote" or merely "wasted ballot".

The problem with b) and c) is that the parties in charge generally don't give a shit about third party voters or people who rejected the ballot. They don't see a reason to reach out to either group, because the voting system promotes absolute dominance, rather than compromise and good representation. Indeed, the media and pundits generally look at third party voting as wasted votes, a mere curiosity at best, and because of how rejected ballots are not recorded, rejecting the ballot altogether would get recorded the same way people who did not vote are recorded.

Our current election system is shit and is one of the worst possible election systems you could choose to use. It's terrifying how widespread plurality voting is.

I don't like Biden much either, and I hate how electing him legitimizes the Democrats basically carrying on as usual without pushing for real electoral reform, but the alternative of letting Trump win is unacceptable. The best move I can see in this election is to tolerate a Biden win and then campaign hard for permanent election reform using Trump's election as a cautionary tale to get a movement going. There's various small groups such as https://electionscience.org and https://www.counted.vote/ pushing for voting reform with score voting based methods, but unfortunately it's hard to get real demand for it unless we can get actual government officials onboard with reform and talking about it publicly.

Assume Trump is allowed back into power because people are unwilling to vote for Biden: the Republicans absolutely will carry on business as usual, as they have demonstrated their will to do so in the impeachment hearing when they had the chance to hold Trump accountable. Allowing Trump back into power as a "piss people off to drive reform" is a wildly risky and bad move that is unlikely to work or be worth the additional years of chaos he'd bring, whereas it's still possible to campaign for reforms even under Biden, since you could easily press for reforms to prevent a Trump scenario from happening again.