The Fujifilm x-t20 RAW is not yet supported in macOS Sierra. See this list:
Digital camera RAW formats supported by iOS 10 and macOS Sierra - Apple Support
But you will be probably out of luck with Aperture, even after the RAW support will be added to Sierra. Aperture is o longer updated by Apple, and none of he RAW support for new cameras that has recently been released for Sierra can be used from Aperture.
You will have to use Adobe's PNG Coverter or the software that came with your camera to develope the RAW files and to convert them to DNG or another lossless format like TIFF to be able to use them with APerture.