What is the ruling on designing a poster for the Arab Women Engineers Forum, and is there any prohibition in it due to the attendance of some women engineers without a mahram, knowing that the design is free of anything that violates Islamic law?

Whoever designs a poster for a meeting or a project forum is not considered an assistant to a woman who will travel to attend this forum without a mahram (definition). The consideration here is the forum itself. If it is held for purposes contrary to Islamic law, or includes forbidden matters, then it is not permissible to design the advertisement, as that would be cooperation in sin.