Go to Theme Settings, navigate to the submenu Performance → CSS, and ensure that the option “Disable default Gutenberg blocks styles” is set to “NO” (disabled). Screenshot (https://monosnap.com/file/6Ck8MY0GiNlQVqNxBUTn4RukEZUbrn). If the option is disabled, but the default block styles are still missing, please provide access to your site so we can investigate this issue from your side.