Unfortunately the CRJ format is not quite the same for the ATR. So the Approach will not be recognized by the FMC.
Solution until Simbrief adds the ATR to it’s export list is to edit the *.FLP:
depending on the approach change
IRwyArrFINAL=I06 into RwyArrFINAL=ILS06
IRwyArrFINAL=L06 into IRwyArrFINAL=LOC06
IRwyArrFINAL=R06 into IRwyArrFINAL=RNV06
or enter the approach manually into the FMC.