North Korea and China both highly favor Biden's  election

 Considering that the Obama administration was viewed by North Korea as timid and unwilling to use force to prevent Kim's nuclear accession, Kim has  decided that Biden offers an easier negotiating partner than Trump.

 Kim also has many other reasons to think that he would  benefit from a Biden presidency in much the same way as that other major nuclear threat-proliferator, Iran. After all, Biden has pledged to return the U.S. to the 2015 Iran JCPOA agreement immediately if he is elected. Considering that the Iran nuclear accord has no intrusive inspections protocols and limitations on Iran's ballistic missile program, Kim  sees that template as one he can most certainly live with.

China, too, is highly likely to play a role here. As recently assessed by the U.S. intelligence community, and judged by an objective comparison of Biden and Trump's respective China policies, Xi Jinping favors a Biden victory. He believes that the Democratic nominee would be less aggressive in constraining China's imperial strategy in the South China Sea and Beijing's global trade agenda. Xi also likely believes he can play Biden as he played Barack Obama and extract American concessions with the reciprocal dangle of carbon reduction commitments (whether Xi lives up to those commitments is a very different matter). And with North Korea highly reliant on China-related trade and diplomatic support, Kim will find it hard to resist any request from Xi, which would be offered in person by a surrogate so as to mitigate U.S. intelligence detection, to display his new weapon or engage in some other riposte of Trump.