If any party has opted composition scheme and the outward supplies made by the him is only of non taxable goods, then where the details of the same should be mentioned in gstr4.
You cant opt for composition scheme if your outward supplies is only exempted. In GSTR4, there is no column/ table to show exempted sales in the offline utility.
If you are dealing with Non Taxable Goods, then you are not liable to take Registration under GST. Refer SECTION 23 of CGST Act 2017 : "PERSONS NOT LIABLE FOR REGISTRATION"...