Then why did God say, “Look, the human beings have become like us, knowing both good and evil. What if they reach out, take fruit from the tree of life, and eat it? Then they will live forever!”? Besides you give no scriptural justification for your idea that it “only” meant “spiritual death”.
Well looking at the Amplified it says “for in the day that you eat of it you shall surely die” and we know that God does not lie. They didn’t die physically that day so it must have been some other way.
I don’t know what the tree of life was, but if you remember the events leading up to the flood, evil people who lived too long were such bad news that He shortened the lifespan of everyone after that as a matter of course. Fallen humans living physically forever would therefore seem to be a valid concern.
Colossians 2:13, Ephesians 2:1-3, I John 5:12 and many more verses discuss the nature of spiritual death as a consequence of sin.