The card supports up to 32 NVMe devices (a hard numerical limit), and provides only 32 lanes of PCIe 5.0 bandwidth to those devices. The switch does give 4 lanes to each device when active, but obviously has to use some sort of multiplexing to do that to all devices. So, you only get 8 simultaneous devices at full 4 lanes bandwidth through the card. If those devices are PCIe 4.0, then the 16 lanes of PCIe 5.0 that connect the card to the slot is also enough for full speed.
Thus, the total 64GB/sec claimed by the card is the most important number. With slower NVMe devices that hit 3GB/sec, the card could support 21 of those devices simultaneously. With PCIe 5.0 NVMe devices at 12GB/sec, then only 5 simultaneous devices would be supported.
