is it permissible to work at a mcDonald's that does not sell
I think your question was sent prematurely.
However, if your question is whether it is allowed to work in a McDonald's that does not Haram products then it is absolutely permissible such in Muslim countries. If a McDonald's does sell a mix of Halal and Haram products then it is better to seek another job which does not require dealing with a mix of Halal and Haram.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America