Does the TrueNAS Mini X+ support NVMe drives in its drive bays?

No, the TrueNAS Mini X+ sticks with SATA-only drive bays, supporting 3.5-inch and 2.5-inch SATA hard drives and SSDs with no NVMe support in the drive bays. It’s a clean, predictable storage setup — SATA drives in, SATA drives out, no surprises.