I've been struggling with belief in God since October 7th. Is it ok to be angry at God?

Yes. It is not only ok — it is one of the most Jewish things you can do. Avraham argued, Moshe argued, Iyov shouted, and the Psalms are full of "how long?" Anger addressed to God is still a relationship with God. The opposite of faith is not anger; it is indifference, walking away without a word. You are still in the conversation, and that matters more than you know.