front page changes when activating polylang

I am developing a multi-lingual and simple site, using Polylang (free version).

My front page should be an static page. Deactivating polylang, the system shows the right page, and uses page.php. Activating polylang it shows all the posts, using index.php

I am not proficient enough to trace how WP decides to what to load; but I suppose that I am misusing polylang in some sense. I would appreciate some hint on how to proceed.

thanks

https://www.ads-software.com/plugins/polylang/