Can anyone recommend an AI solution that is able to retrieve, interpret and synthesize data from SharePoint? Plus points if it's also able to store data in SharePoint in a methodical way based on unstructured data/emails.

For Sharepoint documents the Azure OpenAI model with Azure AI document intelligence service would probably be a good option to look at. It is a private model, has the data protection and DLP capabilities and would be able to access Sharepoint.

We have also got a fair bit of success achieving what you are striving for, using Copilot Studio. If you are enterprise M365 user, you can evaluate for free and once happy with result, can subscribe to Copilot Studio. 

Like below, we are focused in the Microsoft Ecosystem for this with their CoPilots and CoPilot Studio because we get the built in security of the unstructured data, emails, etc for free.   

If you're in the Microsoft ecosystem and need a tool to retrieve, interpret, and organize unstructured data like emails, check out Power Automate paired with AI Builder and SharePoint. Power Automate lets you create automated workflows to pull data from Outlook and store it methodically in SharePoint. AI Builder enhances this by processing unstructured data (e.g., emails, documents) using AI for text extraction, classification, and more.