This process is known as « crawling, » and it’s how Google discovers new pages on the internet.
If your orphan pages are not linked to any other pages on your website, then Google will never find them. As a result, these pages will have zero traffic from organic searches.
Orphan pages can occur for many reasons, but usually, it is because the page has been orphaned during the redesign or development process. It is common for orphan pages to be created when new content is added to the website without properly linking it to other related pages.