Hi @Thangaswamy, Vivek ,
There is no OOB broken link checker in SharePoint Online currently. You can vote for this user voice: Broken-link checker, It is a place for customers provide feedback about Microsoft SharePoint products. What's more, if a feedback is high voted there by other customers, it will be promising that Microsoft Product Team will take it into consideration when designing the next version in the future.
Take a reference to this article if you are looking for a 3rd party tool: SharePoint Broken Link Checker. While Microsoft supports and encourages open-source software development, it does not provide technical support for the software from third parties, nor does it guarantee that the software will work as described.
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