M2A and M2D are the "fast" slots, M2B and M2C the "slow" ones, or as has already been said, the graphics card is only controlled with 8 lanes instead of 16 if something is installed there (but you have such a high throughput with PCIe 5.0 that the loss between 8 and 16 lanes is negligible. I have 4x 2TB and an RTX4090 connected).
This does not matter, but it is important that you only use the top slot of the lower three slots. Otherwise your graphics card will only be controlled with x8 PCI-E lanes. This information is also described in detail in the mainboard manual.