OK. I can’t explain why you need to write to the SLCR_GEM0_CLK_CTRL_ADDR while I don’t need to and the example also does not write to the register. I don’t think it is the responsibility of the user or FreeRTOS to define #XPAR_PS7_ETHERNET_0_ENET_SLCR_x_DIVx if it doesn’t exist because it is the Xilinx driver responsibility.
At this point if you want to debug it further I would recommend that you try to run the linked example code. First check that it works for you and then also step through that section to see what is the path that it takes. Next week I can check again the example make sure what I remember is still accurate.
Have a good weekend.