Generally, if the input-only pin of an IC with a CMOS structure is set to floating, an intermediate potential may be input. This may cause a through current to flow within the device, which may increase power consumption and affect operation.
Therefore, with Intel FPGAs, please make the appropriate connections for each device family.

The Knowledge Base on the manufacturer's website also provides the following information:
[Q] What might happen if an unused dedicated input or unused dedicated I/O pin on my Altera® device is left floating?

Please refer to the pin connection guidelines for each device, which describe how to handle each pin when not in use.
https://www.intel.com/content/www/us/en/support/programmable/support-resources/devices/lit-dp.html