Whether the 2020 presidential election was "stolen" in 2020 as President Trump has charged remains a question, depending on how "stolen" is defined and what is included in the assessment.
There's no doubt there were pockets of corruption, some of which remain unexplained still today. And then there was the $400 million plus in influence money that Mark Zuckerberg handed out to mostly local elections officials who often used it to recruit votes from Democrat districts.
But probably the least contested claim to election manipulation is the case involving the FBI, which tried to influence the election by telling media corporations to suppress accurate reporting about the Biden family's international business scandals revealed in a laptop that Hunter Biden abandoned.