The riser supports PCIe 4.0.
The maximum GPU size is found below:
Note that if the GPU is leaning on to the max length possible in the case (335 mm without SSD mounted in the top front slot. A top front mounted SSD would lower the GPU length by the thickness of the 2.5" drive) you might need to remove the top fan bracket in the case, release the GPU bracket to move the GPU in from the top like in the image above. Most GPUs will however not need to be installed like that and can be done from the side.