Yes, current EmbedPDF has attachment support.

packages/plugin-attachment exposes getAttachments() and downloadAttachment(), and the project site itself ships a PDF Attachment Editor tool. So if your PDF/A eInvoice contains an embedded XML file, the current stack can enumerate and extract that attachment.

The nuance is UI: this is exposed through the attachment plugin/capability, so whether the embedded XML is visible directly in your viewer depends on whether you wire that plugin/UI into the viewer instance you are using.