Could anyone verify if my assumptions are correct?
I think most popular browser(Chrome, Firefox, ...) as a standard send requests with HTTP/1.1 in each request line.
I think whether or not a HTTP/1.1 response is given is determined by the Web server(E.g. a specific version of Apache, Nginx, ...) that hosts the web application. I assume all modern web servers now have HTTP/1.1. If the web server doesn't support HTTP/1.1 I think it will interpret the HTTP/1.1 request as if it was HTTP/1.0 and give a HTTP/1.0 response.