Is it permissible for the one collecting Zakat to benefit from it for himself, given that he is unemployed and lives with his family on a refugee allowance in Europe, and needs money to return and settle in his home country, or is it permissible for him to take it as a debt to be repaid later?

Those who administer zakat (definition) are among the categories entitled to it. These are individuals appointed by the Imam to collect it, safeguard it, and transport it, along with anyone assisting in this process, such as accountants and scribes. However, your act of collecting zakat does not qualify you as one of the entitled administrators unless the ruler of the land or their deputy appoints you.

Nevertheless, if you are poor, needy, or in debt (gharim (definition)), you are entitled to zakat based on these descriptions, provided you are a resident of the country for which the zakat was collected. And Allah knows best.