While we're on that subject, let's do a comparison. From your link...
Mr. Avakian says this is not the year for protest votes, and while he still considers Mr. Biden and the Democratic Party “representatives and instruments of this exploitative, oppressive, and literally murderous system of capitalism-imperialism"
Doesn't sound much like an endorsement. On the other hand, let's look at Trump's endorsements...
Donald Trump on Sunday refused to condemn the Ku Klux Klan or disavow his recent endorsement by former Klansman David Duke.
The Republican front runner said he didn’t know enough about Duke to publicly denounce the former KKK leader, who told his followers earlier this week that voting for anyone but Trump would be “treason to your heritage.”
(Duke, in remarks reported by
BuzzFeed, said he does not support everything Trump has done, but that the billionaire presidential candidate is the best option. Voting for either Ted Cruz or Marco Rubio would be “treason to your heritage,” Duke said.)
“It is your job now to get active,” Duke said, encouraging his followers to volunteer for Trump. “Get off your duff. Get off your rear end.”
“Well, just so you understand, I don’t know anything about David Duke, OK? I don’t know anything about what you’re even talking about with white supremacy or white supremacists,” Trump said on CNN’s State of the Union. “I know nothing about David Duke. I know nothing about white supremacists.”
“I’m just talking about David Duke and the Ku Klux Klan here,” Tapper responded.
The billionaire businessman told the political show’s host Jake Tapper that he’d first need to “do research” on groups in question before saying outright that he didn’t want their support at all. “Certainly I would disavow if I thought there was something wrong,” he said. “Honestly, I don’t know David Duke. I don’t believe I’ve ever met him. I’m pretty sure I didn’t meet him, and I just don’t know anything about him.”
However, Trump had spoken out about Duke, recognizing him as a Klansman, in 2000 when he decided to end his exploration of a run for president, according to the New York Times.
...
At least one of Trump’s rivals criticized him Sunday for not condemning the KKK. “Really sad. @realDonaldTrump you’re better than this,” Texas Sen. Ted Cruz wrote on Twitter. “We should all agree, racism is wrong, KKK is abhorrent.”
Donald Trump Refuses to Condemn Ku Klux Klan
But there is no evidence that Biden has refused to disavow support from any extremist group. This really points up the difference between Trump and Biden.
Trump won't even renounce the endorsement of a Nazi and a KKK leader.