Looks like it was written on an IBM Executive Model A:

https://old.reddit.com/r/typewriters/comments/178vjlf/sample...

There were variable-width font typewriters starting in 1930:

https://old.reddit.com/r/typewriters/comments/3ltlgn/have_va...

https://en.wikipedia.org/wiki/Vari-Typer

That is a REALLY nice typewriter; wow.