Some people wore masks some of the time, varying by seasonality, weighted regionally by the dominant political ideology of the area. My understanding is that masks were more effective against the flu than covid because Covid can spread in finer particles than the flu, which makes masks more effective in fighting the flu.

> people with the flu were testing positive for COVID and health authorities were counting flu cases as COVID.

We know this happens, the critical missing part of your argument is your estimate of frequency. If your theory were true, the precipitous drop in flu cases indicates that almost everyone with the flu also had Covid. That doesn't pass the smell test to me - I feel confident we would have heard if there were that high a correlation, given all the research going on at the time.