A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear Johnny Nguyen,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, it seems that you are trying to add RSS web part in SharePoint to display live cyber security news updates and articles from one of the feeds.
If the understanding above is right, as per the below official article has shared, RSS viewer web part is available only in classic SharePoint, given this, you may need to create a classic site by selecting "Browser more sites" > "More templates" > Team site(classic experience) under SharePoint Admin Center > Active sites > create as a workaround.
For your reference: Add RSS feeds from external sites to your site - Microsoft Support
We hope the above can help. If the understanding above is not consistent with yours, please feel free to post back and point that.
Your understanding and patience will be highly appreciated. We hope that you are keeping safe and well!
Thanks for your cooperation.
Sincerely,
Rhoda | Microsoft Moderator