That’s easy. Having worked in graphic arts in the past, I know that any professional printing operation with multiple modern high-speed offset six color presses could turn them out. Very fast. . . if you need to have them pre-voted just fill in the correct Biden bubbles before creating the print plate (remember the perfectly filled in bubbles on the pristine non-creased, non-folded Biden only, no down-ballot vote, ballots reported seen?) and you’re good to go.
Right. That's my point. States don't mail legit ballots to voters. Their ballot contractors (there are only a handful in the USA) print and mail ballots directly to voters. States don't have big reservoirs of blank ballots laying around, if even one or a dozen.
So if 150,000 ballots for Biden showed up in bulk and at the late hours of morning, they are likely to be fake and identifiable as such.
Failure to exactly (!!!) match the paper and ink used by the legitimate printer would be a dead giveaway.
SO yes you could print something that looks legit on your 6-color offset, but very unlikely that you would have access to the exact same paper and ink.