I am using a 10CL006ZU256I7G FPGA. “I don’t need to use all of the banks in the U256 package. What is the most power efficient way to not use an entire bank?”

Hi , The VCCIO has to connect to required voltage. For unused banks the PCG does nor recommend to connect to GND. Connect to the voltage mentioned as per the guidelines in page no:9 https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/dp/cyclone-10/pcg-01021.pdf