Hello @aryanrajseo,
Thank you for contacting us and sorry for any inconvenience that might have been caused due to that.
Can you please confirm from where you’ve set the category to Noindex? You can try to set the Category Archives Robots Meta Noindex from Rank Math > Titles & Meta > Categories and this setting works for both categories and sub-categories: https://rankmath.com/kb/titles-and-meta/#category-archives-robots-meta-custom-settings
However, please note that this setting can be overridden by the Advance tab robots meta settings in the Rank Math SEO meta box of your category page.
Hope that helps and please don’t hesitate to let us know if you have any other questions.