Sweetened condensed milk can be replaced with unsweetened condensed milk, if you would like to adjust the level of sweetness in the recipe.
Optionally, you can also replace the condensed milk with 11/4 cup of full fat milk and sugar 1/3 cup of sugar.
For a vegan version of gajar halwa, replace the milk and condensed milk with 1/2 cup each of almond milk and almond meal.