Hi Alysha,
I can relate to the challenges of managing archival content in SharePoint Online.
For migrating content from SharePoint Online back to a file share while retaining metadata, I haven't used it personally, but you might want to explore Rclone. It's an open-source tool that supports SharePoint and could be a good fit for your needs with some technical setup.
Regarding your second question, I've created an Archive library in SharePoint for each departmental site with Search turned off. This prevents tools like Copilot and Search from pulling outdated information while keeping archival content accessible when needed. It might be worth considering this option if you want to keep archival documents within your SharePoint environment and retain the metadata.
Your concern about file formats becoming obsolete is valid but having them in SharePoint could actually help in managing file format updates over time. Plus, SharePoint's versioning and metadata management can be invaluable for archival purposes.
Ultimately, balancing budget, technology, and long-term accessibility is tricky, but I hope these suggestions help you explore feasible options.
Best of luck!
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Charles Simpson
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