To know the amount of PCIe lanes you have available , you will have to look for the following:

The first block says that the board will have 8 PCIe lanes. This is generally an extra x16 slot with x8 bandwidth for a dual graphics card slot.

Notice that the second and third blocks read “Pick One.” Manufacturers generally play with this to customize the upgradability of the motherboard. For instance, a particular manufacturer may opt for 4 x SATA ports, and another may opt for a higher number of M.2 slots (each extra M.2 slot occupies 4x PCIe lanes).

The decision is based on many factors. For instance, the size of the motherboard is a factor. While an entirely sized ATX motherboard has enough space to fit in more PCIe slots for add-in cards, the same cannot be said about smaller boards like mATX or Mini ITX boards.

But this chipset, i.e., the X570, offers 16 USER-ACCESSIBLE PCIe lanes: 8 from the first box, 4 from the second box, and another four from the third box.

Also Read: PCIe 3.0 vs. 2.0

CAVEAT : PCIe Lanes on a Chipset Can Be Shared

There are two ways you can use to check how many PCIe lanes your GPU is using:
1. Physical Inspection
2. Using GPU-Z

1. Physical Inspection to Check GPU Lane Usage

On a desktop, through physical inspection, you will need to see which slot the graphics card is plugged into on the motherboard. If it is plugged into the first PCIe slot of your desktop motherboard, then it will almost certainly be using 16 PCIe lanes.

If you have a desktop motherboard with 3 PCIe x16 slots and your graphics card is inserted into the second or the third x16 slot, it will mainly use 8 or 4 lanes, respectively.

This is because, on a commercial motherboard, the second PCIe x16 slot is hardwired to either 8 or 4 PCIe lanes only. The third PCIe x16 slot is mostly hardwired to only 4 PCIe lanes.

2. Using GPU-Z to Check GPU PCIe Lane Usage

Another straightforward and definitive way to check how many PCIe lanes your GPU occupies is through a free GPU-Z application.

This application is particularly great if you want to check GPU PCIe lane usage on a laptop.

The best way to check how many PCIe lanes you are using is to look at the devices plugged into the PCIe slot and also to look at which spaces are occupied.

For instance, if you only have a graphics card plugged into the first x16 slot, you use 16 PCIe lanes. If you also have an NVMe SSD inserted into an M.2 slot, you would use 20 PCIe lanes (a typical NVMe SSD uses 4 PCIe lanes).

If you also have a WiFi card in one of the x1 slots, you use 21 PCIe lanes.

If you also have a 4K video capture card inserted in one of the x16(x4) slots, use 25 PCIe lanes.

To check how many PCIe lanes different PCIe devices occupy, read the following article: Things that can be plugged in PCIe slots .

Excellent info! Thanks very much. This article confirms a lot of what I already thought, but deductions remain assumptions until you read they’re true.
One question I’m still confused about: if I use the integrated graphics from my Core i5 cpu can I use a PCIe expansion card in the (unused) PCIe (‘True’) x16 slot?
Or, on a slightly costlier scale: if I were to build a system with a 48 lane Xeon cpu then those cpu PCIe lanes probably would connect to three PCIe x16 slots on the motherboard, I assume.
Suppose in such a system I would use only one graphics card, would I be able to use the remaining two true 16 lane PCIe x16 slots for other expansion cards?
I’d say why not? But that would be another assumption.
Thanks again!