Critical Warning(18655): There are 6 unused TX channels in the design.

The Quartus Prime software generates a warning message if your design contains unused transceiver channels. The warning message states that performance of unused channels may degrade over time if not properly preserved with the following Quartus Settings File (QSF) assignments - either global or pin specific:

Global Assignment

set_global_assignment -name PRESERVE_UNUSED_XCVR_CHANNEL ON

Pin Specific Assignment

set_instance_assignment -name PRESERVE_UNUSED_XCVR_CHANNEL ON -to pin_name