Breastmilk is the best source of nutrition for the baby. In case not possible you can give home made solid meals slowly as per age. Also include a good formula milk that is closest to mother's milk . Aptamil gold is known to be close to mother's milk. You can try to give that.

Nothing other than breast milk for the baby before completion of 6 months . If breastfeeding isn't an option then look for formula with FOS & Fibre . After completion of 6 months u can start with fruits puree but still breast milk should be the primary source of nutrition

If mother not able to feed, choose Prebiotics and HMO rich FM . Take suggestions with your pediatrician then choose.

You can give ragi malt, or apple you can grind with milk and honey will work and also check with aptmil gold formula milk with HMO AND prebiotics one of the best and complete food for babies to improve the digestion and build strong immune system

Nothing apart from breast milk for baby below 6 months. If mother isn't able to feed the baby then look for formula which contains HMOs and prebiotics and is close to breast milk