In the 2020 election, Trump won in-person voting by 71% vs. 27% for Biden. This was true even in Hawaii and Delaware (Biden's home freaking state).,
Conversely, Biden took the mail-in vote by a 3-1 rate. Even in hard-core Republican states, Biden won the mail-in vote by significant margins (60% in Arkansas and South Carolina!). There was roughly a 60-point variance between in-person voting results and mail-in results between Republican and democrat in 2020. That number in 2016? 14 points.
We all know that the pandemic increased remote voting. That doesn't explain the massive discrepancy in voting results between methods.