According to Chatgpt:
In the 2020 election, approximately 90.7 million mail-in ballots were requested, around 75.7 million were used, and about 15 million went unused.
In the 2024 election, as of November 5, over 65.6 million mail-in ballots were requested, with 25.9 million used and about 39.7 million still unused at that time.
What happened to those 39.7 million people that wanted to vote? Could this be a clue to Harris's missing votes?
Personally I think the original methods were a one trick pony, hence why they could be stopped in 2016.
In 2020 they diversified their cheating methods so it would have been whack-a-mole and the WH's used 2020 to map all their new methods so that they could co-ordinate and stop it in 2024.
Trump has said that they "caught them". This before the election. So your theory sounds about right.