I'm trying to figure out how to get opening rates (not the list of the people that opened the mailing) for our newsletter mailings.
Thank you.
Welcome to CiviCRM SE.
In the menus go to Mailings > Scheduled and Sent Mailing, which lists all the mailings. On the line for the mailing in question and click on Report. This gives you what you are looking for.
Under Reports > Mailing Reports you will see one for Open and one for ClickThrough.
If you want aggregated data per Mailing then you may need to have a look at SearchKit