Combine cold brew coffee, milk, sweetened condensed milk, sugar, vanilla, and salt in large measuring cup.
Whisk until sugar dissolves and everything is combined.
Taste. Adjust sweetness. Should taste slightly sweeter than desired final flavor.
Stir in mix-ins if using.
Pour into popsicle molds. Fill to ¼ inch from top.
Place lids on or cover with foil.
Insert sticks through lids or foil into center.
Place in freezer on flat surface.
Freeze at least 4 hours or overnight until solid.
Run warm water over molds for 15 to 20 seconds to release.
Gently pull out popsicles.
Serve immediately or wrap and store in freezer bag.