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.
I'm fairly sure that climate change denial, a belief that marriage equality is wrong etc are not protected under the Equality Act, because they don't meet the Grainger test. Of course, if they constitute part of a religious belief, they would be protected, because religious belief is protected under the Act.
You can read more about the Grainger test, and what constitutes a protected belief, here:
https://commonslibrary.parliament.uk/employment-tribunal-rulings-on-gender-critical-beliefs-in-the-workplace/#:~:text=The%20Grainger%20criteria&text=(i)%20The%20belief%20must%20be,of%20human%20life%20and%20behaviour.