I check full width in the theme options, but the sidebar is still visible.
Everything is fine on the home page,
but the category pages still show the sidebar
The settings you have applied refer to the category pages like this one:
This is a single post: https://skorna.pl/specjalista-to-zobowiazuje/
You can disable the sidebar for the single posts by editing each post individually and assigning the preferred layout for it in the Post Layout section.