I suggested the creation of a new profile, that I named "user", from the "guest" role allowing to do the things we need in the main page.
This worked well for a forum activity but I tested it with a choice and I see the problem you explain. I supposed that the problem was in the source code and not in the roles, so I take a look to the php files in choice folder.
I found that in order to make the table with the answers to the choice, the report.php and lib.php files use the get_course_users function to fill the $users variable. This function relys on the moodle/course.view capability, so the users with the "user" profile I created were not found.
I changed the function to:
$users = get_users_by_capability($context
, 'mod/choice:choose', 'u.*, ul.timeaccess as lastaccess', 'ul.timeaccess DESC', '','','','', false);
and it seems it works...
If you give it a try, tell me about the problems that this change can cause. I'm not a great programmer and I don't know very much about the programming issues with moodle. This is my second attempt to modify the source code, so be careful.