...Trump: "We have anywhere from 250 [thousand] to 300,000 ballots were dropped mysteriously into the rolls, much of that had to do with Fulton County, which hasn't been checked."

Fact check: Trump's made-up claims of fake Georgia votes (January 2021)
www.mprnews.org
The facts: There's nothing mysterious or suspect about it. He is describing a legitimate vote counting process, not a sudden surge of malfeasance.

Trump appears to be referring to large numbers of votes that were tabulated in the early hours of Wednesday morning after Election Day and later. The arrival of those votes was not mysterious, but expected, because many of Georgia's 159 counties had large stacks of mail-in ballots that had to be tabulated after polls closed and in-person ballots were counted.

Indeed, news organizations and officials had warned in the days leading up to the election that the results would likely come in just as they did: In-person votes, which tend to be counted more quickly, would likely favor the president, who had spent months warning his supporters to avoid mail-in voting and to vote in person either early or on Election Day.

And mail-in-ballots, which take longer to count since they must be removed from envelopes and verified before they are counted, would favor Biden. States tend to count mail-in ballots at the end of the process. ...

www.mprnews.org