Debunked quite a few times. Every state is responsible for printing their own ballots and every printer has a unique watermark.
Of course the states print their own ballots, however, it's not 100% impossible that Trump couldn't have had allies in place at the state level to affect such a sting. Stranger, more bizarre things have happened just in the last 4 years alone.
Does DHS provide watermarked blank paper to the states for them to print their own ballots?