@lanodan Since NVMe is PCIe in a different form factor, multi-drive adapter cards are either very simple but require PCIe bifurcation from your BIOS (not necessarily available) or quite expensive because they need a PCIe bridge/switch/etc to multiplex multiple downstream NVMe drives onto one set of PCIe lanes.
(The cheap require-bifurcation ones just split eg x16 PCIe lanes to 4 x4 sets and wire them to four NVMe drive slots.)