I was trying to craft a steel weapon, I have the handle and the steel as the item was looted from a chest but when I go to craft it, it won't let me.

UPDATE: The Steel is from the Modern Structures mod looks like. But there's no steel, tin, or anything from the Spartan Weaponry mod.

Picture below.

I have the same problem, some materials like steel, nickel, silver say they are missing, I don't know which mod to put to add these minerals

The Modern Structures version of Steel is not in the Item Tag "forge:ingots/steel". You will either need to ask the developer of that mod to add the item to the tag, or you can do it yourself with a datapack, if you're comfortable with that. This is something I can't fix myself.
Closing issue.