How to display/not display grades on the report card to students and parents?

The school administrator can choose whether the grades on the report card will be displayed to logged-in students and parents.
You can set this in the Pedagogical documentation - Certificates / transcripts section.

You can publish report card grades to the entire school at once: you mark your classes and click publish grades,

or you publish grades only to selected classes.

You can find the current status of how many grades are published at your school here: