I don't think Harris accurately portrayed what happened but it looks like this article and your comment also don't accurately portrayed it. I don't think its right (or even necessary here) to counter misinformation with more misinformation.
There's no evidence Lincoln didn't appoint a Judge because Congress wasn't in session provided in this article or anywhere. If he really wanted to, Lincoln could've called a special session (which has been done to confirm cabinet appointments).
I think the below links provide decent explanations although we probably won't know his exact reasons. It seems likely though it wasn't to let the people decide in the election.
https://www.lincolncottage.org/lincolns-election-year-supreme-court-nominee/ As ever, Lincoln was the shrewd politician and in October of 1864 he saw no profit in alienating any of the factions of his political support by making a selection before the election. There is no evidence that he seriously considered announcing his choice before he was re-elected.
https://www.washingtonpost.com/history/2020/10/08/lincoln-supreme-court-kamala-harris/ Lincoln was preoccupied with both his campaign and the Civil War — Sherman’s troops had just captured Atlanta and would soon march to the sea. He told his aides he wouldn’t nominate anyone immediately, because he was “waiting to receive expressions of public opinion from the country,” according to historian Michael Burlingame in “Lincoln: A Life.”
But that didn’t mean he was waiting for ballots so much as the mail. Letters flooded in from all over the country.