https://prnt.sc/11iyyq5
I can not produce steel. What have I missed?

K2 has disguised its furnaces, but they are in fact assembling machines (which allow more than one ingredient in recipes).
It means there are no vanilla electric furnace, where this mod is supposed to support with.

I guess it is better if K2 scans for all furnaces (with matching recipe category) and convert with their overhaul method. Currently K2 is just hard-coded converting the three vanilla furnaces only.
You may ask if K2 is willing to improve that.

since i don't understand the problem completely (I would have to know both mods), i can't really explain it well to the K2 author, that would be more your task i think ;-)
As a naive solution, I would actually just write a new scaled recipe. is that not possible?

It is not that complicated.
The real furnaces (type "furnace") can only take one ingredient and one product in their recipes. So vanilla furnaces can be fed with both iron ore and copper ore as mixed input and producing their plate form, without the need to assign recipes by hand.
On the other hand, K2 steel (as what you have posted) takes multiple ingredient, which won't work in vanilla furnaces. So K2 just replaced all vanilla furnaces as assembling machines (type "assembling-machine"), disguising them as their original.

The problem comes from:
Even though K2 is overhauling the whole vanilla furnace system (as the above-mentioned replacement), they are assuming the three vanilla furnaces are the only ones you have in game. They don't care about any other (modded) furnaces that are doing vanilla smelting. From reading its code, I presume EVERY modded furnace (that can smelt iron ores & plates for iron plates &steel plates) will be ignored and thus not working. My furnace is just one of its "victims".

A solution seems rather simple. In K2 entities-changes.lua, function transferFromFurnacesToAssemblers should be applied to any furnaces which are also doing the vanilla "smelting". Not just the three vanilla furnaces.
I do not write K2 code, so I am not sure if this solution may work or not.

Sorry for the super late response, but I went ahead and made the change. Hopefully it doesn't break compatibility with everything else...

Thanks. I have very little time for games at the moment, but I'll see if I can manage at least a short test.

Thanks also, i raised the git hub request to push this as well, i have been using it for 2 weeks now works great. One thing to watch is on update all existing furnaces are replaced and you need to re-select there recipe if you were using them for copper/iron for example as the recipe now needs to be selected.