1st of all, any role with access to the wp-admin (Dashboard) should have a ‘read’ capability.
Some plugins, like WooCommerce restrict by default access to the WordPress back-end. Do you have active WooCommerce?
Look if you have some other plugin with similar option, for example Ultimate Membership. It requires apparently allow access to dashboard for selected role(s). You can try to deactivate all plugins except LearnDash and try. The activate plugins one by one to isolate which plugin prevents access to the WP backend.