Is it permissible to work in customs in an Arab country that does not rule by Allah's law? Is this considered a form of illegal taxation (maks)? And what is the ruling on working in a medical department affiliated with the customs administration?

The permissibility of working in customs depends on the permissibility of the customs duties themselves. If the customs duties are in exchange for services or for a legitimate public benefit that the state's resources cannot cover, then they are valid and permissible (halal). However, if they involve taking people's money unjustly, or without the state's need, or if the amount taken is excessive, then they are forbidden (haram) and considered grave sins. In this latter case, working in customs is impermissible, and earnings from it are forbidden. The most cautious approach is to avoid working in customs if its permissibility is not clear.