If you navigate to Rentals > Amenities you will find the whole list of amenities available in BookingSync:
For each amenity, you can choose if it is searchable and/or visible.
searchable amenities are displayed as criteria in the search bar of the home page.
visible amenities are displayed in the amenity section of each rental page, no matter if they are checked in BookingSync for this rental or not. Then, the amenities checked for the rental appear in dark grey whereas the non-checked amenities appear in light grey.