I'm pretty sure that the mystery slot on the back of the Xbox Series X is a CFexpress memory card slot. If an ethernet port is about 11.5mm wide then using the
Xbox Series X mystery port is for CFexpress cards claims latest rumour | Metro News
Amazon.com: NFHK CF-Express Type-B to M.2 NVMe 2230 M-Key Adapter CFE for Xbox Series X&S CH SN530 SSD PCIe4.0 Expansion Memory Card : Electronics
It may be possible to use an M.2 SSD through and adapter similar to CFexpress : r/XboxSeriesX
Xbox Series X/S appears to use modified CFexpress interface for external storage | ResetEra
Amazon.com: NFHK CF-Express Type-B to M.2 NVMe 2230 M-Key Adapter CFE for Xbox Series X&S CH SN530 SSD PCIe4.0 Expansion Memory Card : Electronics
/cdn.vox-cdn.com/uploads/chorus_image/image/66248918/Xbox_series_X.0.jpg "Xbox Series X may get fast expandable storage with CFexpress cards - Polygon")
Xbox Series X may get fast expandable storage with CFexpress cards - Polygon
Xbox Series X Expansion Slot Is for a Proprietary Storage Expansion Card
/cdn.vox-cdn.com/uploads/chorus_asset/file/19619952/Xbox_series_X.jpg "Xbox Series X may get fast expandable storage with CFexpress cards - Polygon")
Xbox Series X may get fast expandable storage with CFexpress cards - Polygon
CY CF-Express Type-B to NVMe 2230 M.2 M-Key CH SN530 SSD Adapter CFE for XBOX Series X&S PCIe4.0 Expansion Memory Card - Walmart.com
The Xbox Series X expansion card: a CFexpress? | The Output
XBOX Series X/S Host Hard Disk Adapter CFexpress Convert To M.2 SSD Aluminum Alloy Case Xbox S To CH SN530 Memory Card Converter - Newegg.com
Amazon.com: NFHK CF-Express Type-B to M.2 NVMe 2230 M-Key Adapter CFE for Xbox Series X&S CH SN530 SSD PCIe4.0 Expansion Memory Card : Electronics
Western Digital Unveils Xbox Series X|S Expansion Cards
CFexpress To SSD M.2 NVME For Xbox Series X/S XSX To SN530 1TB Replacing Seagate | eBay
Modder expands Xbox Series X/S NVMe SSD with CFexpress adapter
Western Digital Unveils Xbox Series X|S Expansion Cards
Modder uses CFexpress adapter to attach Xbox Series NVMe SSD as expandable storage - VideoCardz.com
CFexpress To SSD M.2 NVME For Xbox Series X/S XSX CFexpress To SN530 1TB os67 | eBay
Conversion Adapter Lets You Install Short M.2 SSDs Into Xbox Series X, S | Tom's Hardware
Newest ESXS Xbox Series X|S XSX XSS CFexpress to M.2 1TB Memory Card
Ssd Cards Xbox Series X | Hard Disk Ssd Xbox Series | Cfexpress Nvme Adapter - Card Hard - Aliexpress
Topcine CFExpress B to WD SN530 SSD Storage Expansion Card Adapter for Xbox Series X/S
