Supported Minecraft Versions:

• 1.17

Basic Skript made in 5 minutes for smelting,
How to add more? [Advance!]

Spoiler: Steps on adding more

1st. Add one to the list in syn on options
2nd. copy this:

Code (Text):

1.         if arg-1 is set:
2.             if arg-1 is "SMELT":
3.                 if player has SMELT:
4.                     message "&3&lSmelting SMELT.."
5.                     remove 1 SMELT from player's inventory
6.                     wait 1 second
7.                     message "&3&lSmelted SMELT!"
8.                     give player 1 SMELT

3rd. replace SMELT with your block of choice
4th. put it in the next line of code.
5th. Go to line 26 and if you see [if arg-1 is not "cobblestone" or "iron"] add one more like this, [if arg-1 is not "cobblestone" or "iron" or "SMELT"] and replace the smelt with the block of your choice that is similar to where u put [ if arg-1 is "SMELT": ] and you are done!

DISCLAMER:
THIS IS NOT SUPPOSED TO BE A GOOD SCRIPT. THIS WAS MADE IN 5 MINUTES SO DO NOT COMPLAIN IF ITS BAD! Thank you!