Is watching Arabic movies on TV or the internet forbidden (haram), even if they do not contain anything that violates morals, and is entering a cinema forbidden (haram), even if it is for entertainment once a year?

The permissibility of watching movies and entering cinemas depends on the extent of their adherence to Islamic legal rulings, such that they do not contain forbidden elements like obscenity, nudity, prohibited singing, or immodest display (تبرج). If they meet these criteria, then watching them is permissible. Otherwise, it is not permissible to enter a cinema to watch movies that violate Islamic law, whether that is once or repeatedly, and whether on Eid or other days.