NVMe: booting would require a UEFI mod, although there are workarounds if it's a legacy BIOS. With no discrete GPU the x4 PCIe 3.0 slot can be used for an adapter, otherwise x1 PCIe 2.0 (which is slower than SATA sequentially but still provides latency benefits). There are vertical adapters, low profile adapters, and shorter SSDs. I actually did this mod on a B85 board for a Steam Deck post with a link to the adapter. Enclosure + USB may be possible also but not ideal. You can't convert NVMe to SATA (exception is some boards with SATAe, but that's still not SATA).