Holding a gender critical belief is protected, as are the belief that gay people are sinful, that marriage equality is wrong, and that there are differences in intelligence between races, as, I suspect, is climate change denial. However, there are many circumstances in which expressing or acting on those beliefs are discriminatory and grounds for dismissal - for example, misgendering or deadnaming transgender employees or clients.
Employers are going to have to be a lot more careful in future.