On the DDI monitor,/ HSI screen the ILS button generates message “not implemented” and on the UFCD monitor the “D / L / BCN / ILS” button does not work.
I’m not entirely proficient in ILS (I use Garmin to start ILS in DA40 / 62 or Dahler ) but I expect that I should at least have a place where to enter the ILS frequency?
From discussions around the DCS F18, although they may be fitted with an ICLS system, for landing on carriers, RL F18s might not be equipped with land-based ILS systems.
Whether this MSFS F18 does or not, you might want to ask the developer.