IMO, there's nothing wrong with mail in voting. I mailed in my ballots for most of the last 20 years.
I know it's easy to say just throw a mask on and go to the polling place but it's not that easy for a lot of minority and poor people. Gerrymandering and calculated closing of polling stations is a real deal. It's not a coincidence that "certain" areas have more polling stations with much shorter wait times and working voting equipment compared to other areas.
If you're white and live in a suburban area the time it takes you to vote is much, much shorter than it is in black/minority neighborhoods. There have been quite a few studies that have pointed this out.