The text shown is not a normal download link. sandbox:/mnt/data/... is a temporary internal location used while Copilot creates the file, so it cannot be opened through File Explorer or searched for on the device.
Please return to the original Copilot conversation and ask Copilot to regenerate the presentation and attach it as a downloadable .pptx file. If the original conversation or attachment is no longer available, the presentation may need to be created again.
Hope this helps, please feel free to let me know if you need any further assistance
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