Hi@AkshayAuradkar,
Based on the issue that you mentioned, do you want to update the SP list within the Portal?
Could you please share a bit more about the scenario?
If you want to implement to update the SP list within PowerApps Portal as an external user, I am afraid that there is no way to achieve this currently in PowerApps.
As we know, Dynamics 365 Portals version 9.0.10 for the customer engagement apps brings some new updates and features for earlier. And one of them is Manage SharePoint documents.
Dynamics 365 Portals now supports uploading and displaying documents to and from SharePoint directly on an entity form or web form in a portal. This allows portal users to view, download, add, and delete documents from a portal. Portal users can also create folders to organize their documents.
Although this is an update to SharePoint, it is still based on CDS as a whole. This update simply adds the feature of the document management capabilities.
For more details, you could check the following article for reference:
https://docs.microsoft.com/en-us/powerapps/maker/portals/manage-sharepoint-documents
For more about the released updates, you could check the following article:
https://docs.microsoft.com/en-us/powerapps/maker/portals/release-updates
Here is the article that lists all of the updates that have been made to portal capabilities for Microsoft Dynamics 365 to date:
https://support.microsoft.com/en-us/help/3181191/portal-capabilities-for-microsoft-dynamics-365-releases
Best Regards,
Qi