Am I sinful for delaying the payment of Zakat al-Mal for six months—until returning to my home country where poverty is more widespread—due to uncertainty about who is eligible to receive it in my current country of residence?

Zakat (definition) must be paid promptly once the wealth reaches the nisab (definition) and a full Hijri year has passed. Whoever delays it without a valid excuse is committing a sin. Strive to find those who are eligible, and if you are unable to do so, you may entrust a reliable person to distribute it in your country or another country. It is permissible to transfer it out of necessity. However, if you are unable to pay it or entrust someone after making an effort, then there is no sin upon you for delaying it until you are able to do so.