Comparing Translations
"Which one is the correct one?"
One of the challenges in interpreting the scriptures is that we cannot always be 100% confident of what the original authors intended when they wrote down the words in front of us. Longman and Shields have both called this verse "one of the most difficult verses to interpret in Ecclesiastes", so be wary of anybody who gives you an easy answer to this.
If you look at a comparison of different English translations, you'll see a wide variety of approaches. The Amharic translation seems very close to that of the King James:
He hath made every thing beautiful in his time: also he hath set the world in their heart, so that no man can find out the work that God maketh from the beginning to the end.
Similarly, the New English Translation of the Septuagint (NETS) follows this reading too:
He made everything fine in its right time; indeed he granted eternity in their heart so that they should not find the work that God has done from the beginning even to the end.
So there is certainly a strong historical tradition aligning with how the Ahmaric translation has rendered it, though obviously modern translators are still split on how best to render this verse.
Conclusion
Although the "so that" looks like it could be right enough, I think there may be a different issue with the Amharic rendering, because it seems to be missing the concept of having "eternity in the human heart", which is common to the vast majority of English translations. I'm not sure if perhaps your translators have moved this to before or after the verse you've quoted, or whether they've left it out completely for some reason.
To me this is the key to the causation - that God placed eternity in men's hearts so that they would not be able to fathom his works. Missiologists have talked about this as an inner mystery or hope which all people inherit at birth, which causes them to seek after God.
After-thought
From this and some of your other questions, I am wondering if perhaps you are alarmed to discover that some translations render some verses quite differently to others, and that does create a real question of "when I teach from the scriptures, what should I trust?"
If you consider Ecclesiastes scripture, I would suggest that this should not become a scary idea, because this can drive you deeper in how you read and interpret the text. By questioning and checking the translations in front of you, you will continue to become better equipped to study and understand every word. Where we see things which we think are "vital" differences, this should remind us of the importance of not creating teachings based solely on one verse, and why we must understand and teach from the whole of the scriptures, to prevent minor mis-understandings from impacting our understanding of the whole.
