There is no evidence to suggest that polls were conducted in a way that deliberately presented Joe Biden in a favorable light.
Citing the Quinnipiac poll released before the election day, he said, "To highlight just a few examples, the day before election Quinnipiac which was wrong on every occasion that I know of had Joe Biden up by 5 points in Florida and they were off by 8.4 points and I won Florida easily," Trump said. "They had my losing Florida by a lot and I ended up winning Florida by a lot...other than that they were very accurate." He also criticized The Washington Post poll.
The relevance of pollsters as a predictive tool was heavily scrutinized in 2016 after the election results which were widely divergent from what the opinion polls had predicted. While major pollsters like Real Clear Politics and FiveThirtyEight are being widely criticized for their inaccurate predictions this year as well, Trump's allegations insinuating that pollsters deliberately favored Democratic Presidential nominee Joe Biden is a stretch. There is no evidence to suggest that any of the major polls were operating at the behest of the Democrats. The Post called Trump's claim a conspiracy theory. Also, Trump has garnered more votes in various states than what many polls had predicted pre-election.
A study conducted by the Pew Research Center analyzed the limitations of polling and explained that the real environment in which polls are conducted bears little resemblance to the idealized settings presented in textbooks. Andrew Mercer, a senior methodologist at the Pew Research Center told The New Yorker that polls tend to vary because "there are a lot of subjective decisions about how to go about things that different pollsters do differently for a variety of reasons."
NBC Connecticut reported that Doug Schwartz, director of the Quinnipiac University Poll, responded to Trump's comments, saying they stand by their methodology. He said, "For more than two decades, the Quinnipiac University Poll has been a highly-trusted source of opinion surveys with a stellar track record,” Schwartz, said in one statement. “We stand behind our methodology and the polling industry provides valuable insights into changing political opinions over time. We learn with each election cycle and our experts will examine our polling methods and make any necessary adjustments in future years. A full examination of what went wrong with polls this year is going to take a while. At the moment, I still need to see the final election results and final exit poll results, and without those, I am not able to make even preliminary hypotheses about what exactly the issues are," he said in an email.