This is not an original addon, just a port to the 1.21.1. You can find it at https://www.curseforge.com/minecraft/mc-mods/create-molten-metals . While being a port, this mod also adds better compatibility with other mods, unlike 1.20.1 version.

Do you have a Tinkers' Construct shaped hole in your heart? Why not fill it up with some Molten Lead!

Create: Molten Metals is a lightweight create addon with one goal in mind: let you melt down metals and and pour them back out into ingot molds. With a significant (and ever expanding!) list of compatible mods, this is the best place to go for modpackers looking to create an expert experience through the power of Molten Metals.

List of currently supported metals:

Iron

Gold

Copper

Netherite

Zinc

Brass

Mod compat metals

Lead

Electrum

Silver

Necromium (Caverns & Chasms)

Bismuth (Etcetera)

Mercury (Spelunkery)

No ingot, bucket only

Tin

Bronze

Steel