Having used this guide
https://gbatemp.net/threads/tutorial-setting-up-9-0-9-2-n3ds-xl-for-rxtools-cfw-including-emunand-coldboot-cia-manager.405589/
I'm now finally done, but when trying to boot a .cia in FBI, it says
Install failed!
TTCDF0JAPRFCIA.cia
source: SOURCE_FSFILE_WRITE (0x1c)...