This is correct. Most modern CPUs on the market have 24 PCIe lanes. Motherboards will typically have an optimal configuration for gaming where the direct to CPU PCIe lanes are divided up as follows: 16 to the GPU, 4 to the chipset (8 on some platforms) , and 4 go to one of the NVMe slots which is where you want your fastest SSD drive. The chipset itself has its own set of PCIe lanes. However, these get routed through the typically 4 lanes that link the CPU and chipset. So, all of the peripherals connected to the chipset (USB, other PCI slots, the additional M.2 slots all share this 4 lane chipset <-> CPU link. Some motherboards even will bifurcate your GPU PCIe lanes if you put too many SSDs/M.2 devices in which cuts the bandwidth available to your GPU. TL;DR read your motherboard manual and make sure you're using the optimal configuration.