From the Wall Street Journal:

https://www.wsj.com/articles/putin-authorized-influence-operations-to-hurt-bidens-2020-candidacy-report-says-11615918958

"Russian President Vladimir Putin authorized operations last year
intended to hurt Joe Biden’s presidential campaign and support
President Trump’s re-election while sowing discord to exacerbate
tension in the U.S., a U.S. intelligence assessment released Tuesday
said."
..
..
..
"Russia’s efforts relied on proxies linked to Russian intelligence
services, which promoted “influence narratives—including misleading or
unsubstantiated allegations against President Biden—to U.S. media
organizations, U.S. officials, and prominent U.S. individuals,
including some close to former President Trump and his
administration.”

Of course this begs the question of why Putin favored Trump over
Biden. Neither the WSJ or the intelligence assessment addressed that
important question. There has been speculation in the past that
Russian intelligence had compromising information on Trump but those
allegations have bever been proven. It's well known however that
Russia helped Trump secure financing for his business interests after
US banks refused to lend him more funds.