Move focus to the hamburger for the drawer. It should read as a button and should say expanded or collapsed. enter or space should expand the drawer and shift focus to it so you hear "navigation region". tab should then take you through the navigation links.
Test with JAWS
Move focus to the hamburger for the drawer. It should read as a button and should say expanded or collapsed. enter or space should expand the drawer and shift focus to it so you hear "navigation region". tab should then take you through the navigation links.