You may see this pin placement error in the Intel® Quartus® Prime Software if you have enabled the Passive Serial (PS) configuration scheme and assigned the DCLK pin as a regular I/O pin. You can only assign the DCLK pin as a regular I/O pin if you selected the Active Serial (AS) configuration scheme. When the Passive Serial configuration scheme is selected, the DCLK pin can only be used as a programming pin.
Change to the Active Serial configuration scheme or remove the user signal location assignment to the DCLK pin.
Refer to the Device Pin Connection Guidelines for further details.