QNAP do a compact NAS with 4xM2 slots. It's not cheap and it's probably not exactly what you meant by SBC though... https://www.qnap.com/en/product/tbs-453dx h

QNAP do a compact NAS with 4xM2 slots. It's not cheap and it's probably not exactly what you meant by SBC though... https://www.qnap.com/en/product/tbs-453dx https://www.qnap.com/en/product/tbs-453dx (edit - they aren't nvme slots as I first said, they're m2 sata)