Ryzen 9 5900XT & PCIe bifurcation

So I'm going to try doing a new PC build after 8-9 years...I need a new one.

I want drive/CPU heavy, but gaming capable, aiming for $1500ish (reusing case/PSU I already have). I think I'm settling on the AMD Ryzen 9 5900XT CPU, but trying to figure out how the PCIe bifurcation works as I'd like to do 4x M.2 drives in RAID10 to really max out that drive performance.

So that gets me to the PCIe lanes actually available. 4x M.2 drives will use 16 lanes. The amd page says for the CPU says there are "20 usable lanes", does that mean I'm going to be stuck with 4x for the GPU? The amd page also says:

Additional Usable PCIe Lanes from Motherboard: amd_x570 16x Gen 4

Does that mean with an x570 chipset, I can get 20 lanes from the CPU, and 16 from the chipset? That would let me run the GPU and all the M.2 at full speed with still 4x available for another expansion card? If yes, what motherboard supports that?

If no, is there anyway I can get an 8x GPU and 16x for the M.2? All I found so far is threadripper, I don't know I can fit that into my budget.