Yes, I have heard of this. And it's a thing that happens. You can see it in the 2020 race too where Republicans won the house/whatever race but Biden won the district. it's why there was a big focus on Georgia in 2020, because it happened to Trump. Drop Off happens.
When things like this happen, we go looking for explanations on why we lost the race we felt we should have won. The easier answer is "they cheated" and the drop off makes it seem like they did. Because if they voted democrat down ballot why wouldn't they also just fill in Harris?
But the harder, and more accurate, reason is they did leave it blank on purpose. Whether its because of misogyny, racism, anger at Biden, a desire to "send a message" over INSERT CAUSE, the result is the same, they didn't fill it in on purpose.
If you think about it and focus on it for too long you'll start chasing your own tail, and then all of a sudden your insisting on voter security and all sorts of things. Which is how normal conservative people ended up in MAGA post 2020.
Do I think they cheated and somehow removed the votes? No. Because the down ballots won. Trump isn't subtle or that smart. He would have had a Reagan/Nixon level victory with a clean sweep in the house & senate.