Every data connection has two limiting factors shielding and wire length/connection count. If the shielding is bad you have cross talk between two close data wires or external influces that can corrupt the data packages. PCIe 4.0 has very high frequencies that limit the signal length because after some inches the signal and clock is out of shape, also every physical connection reduce the signal quality so you need a retimer or redriver to rebuild it.
The max length for PCIe 4.0 is 10inch this is 254mm. The A4-SFXv4 riser is 185mm so we have ~70mm from CPU to PCIE socket and GPU to riser socket. There is a bit of hope that this will work. With a bit of luck the Gigabyte x570 ITX has a retimer infront of the PCIe socket than it could be work.