Is it really dead code, or we haven't found out what it does?

Since you’ve only been told that you’re wrong, and I was also under the impression that there was a lot of junk DNA in our genome, I did a little digging and found this article that explains the progression of our understanding pretty well: https://www.sciencenewstoday.org/human-dna-98-of-your-genetic-code-is-junk-or-is-it

The TLDR is that the original junk DNA hypothesis is based on the fact that only ~2% of DNA is actually used in mapping out protein-construction. That was generally supported by the science from the 70’s to the early 2000’s. What scientists have found in the decades since then is that a lot of what DNA does involves regulating activity in the cell and responding to changing circumstances.

That's a very outdated idea.