In my country, Serbia, there is still vivid memory of typhoid fever. There was a saying from 1914/1915:

Don't worry people, General Typhus is protecting the borders!

Indeed, the battles stopped during the epidemics.

Later, during Spanish flu, many people died, especially young and children. Again, there is a saying:

Spanish girl took them (Shpanyolka took our young boys)

It would be just strange and odd that people remember both epidemics, but none of them is mentioning masks.

We also remember nurses from England and France who came to help, we remember Swiss doctors, there is a lot of stories about them and yet... Not a single one ever mentioned something bluntly obvious that all of them used to wear masks all the time.

In my country, I can guarantee that it never happened.