Hello,
I got extasic when I heard about OC2! I still use 1.12.2 due to individual mods compatibility.
Is it possible to port it to 1.12.2?

It is possible, but backporting a mod takes a lot of work, and nobody is doing it right now. (see this comment)

1.12 is a complete rewrite of the java code. There is so much of a technical change a Backport doesn't make sense.

1.14 could be possible.
But everything before is really not feasible.

And the normal open computers exist on 1.12.2

I won't be backporting this.