During the Singapore summit, Trump gave Kim a glimpse inside his presidential state car -- a $1.5 million Cadillac also known as "The Beast" -- in a show of their newly friendly rapport.
The Trump administration argued that it ended a diplomatic logjam and effectively stopped North Korea's nuclear and missile tests, although critics say that Pyongyang nonetheless advanced on the programs.
Biden has said a response to climate change will create new jobs, while Moon has introduced his ambitious Green New Deal aimed at economic recovery from the coronavirus fallout.
The process has been stalled ever since, while the North has showed off several new missiles at military parades in October and earlier this month, when Kim pledged to strengthen its nuclear arsenal.
"It looks like the number of (North Korean) people entering the South decreased due to the effects of North Korean-Chinese border control and restrictions of movement from third countries due to Covid-19," Seoul's unification ministry said in a statement.
Moon said the issue of joint South Korea-US military drills, which Pyongyang has long condemned as a rehearsal for war, can be discussed by reviving an inter-Korean military panel.
North Korea has not reported any confirmed cases of the coronavirus, but it has imposed strict border closures, domestic travel restrictions, and other measures to prevent an outbreak.
North Korea's economy shifted away from being fully centralised after many private markets and business sprung up in the face of government failures to provide in the 1990s.
Satellite imagery showed that "preparations for a parade appear to have stepped up a pace", according to the respected 38North website, just months after Pyongyang showed off by far its biggest missile yet.
Biden's victory and Bolsonaro's reluctance to recognize it have cast a dark cloud over US-Brazilian relations, which had warmed to the point of discussing a free trade deal last year.
Talks over the North's nuclear arsenal have been stalled since early last year when a summit in Hanoi between President Donald Trump and leader Kim collapsed over what the North would be willing to give up in exchange for a loosening of sanctions.
Harry Kazianis, a North Korea expert at the Center for the National Interest think tank in Washington, said the Kims and several senior North Korean officials had been vaccinated.
The effort focuses on boosting production of unspecified materials and equipment, harvesting seasonal crops, storm relief work, and steps to prevent any virus outbreak, KCNA added.