I still want to acknowledge that some people believe in gender identity and that is real to them
Gender identity isn’t a belief. It’s the sense someone has that they are male, female, both, neither, etc.
It’s possible to have beliefs about that sense, and there are numerous different beliefs people can have about it, but gender identity itself isn’t a belief.
If you believe your sense that you are male, female, both, neither, etc is because you have a pink, blue, some other colour brain, then that’s a belief. If you think you ‘just know’ you are male, female, etc magically without using your senses to sense your body characteristics, that’s another belief. There are many more.
The way you have talked about wanting to acknowledge that some people believe in gender identity sounds odd, and like you don’t understand what gender identity is at all. Like if you said I want to acknowledge that some people believe they have a sense of being British, but you’re either born in Britain or you aren’t; there’s no such thing as having a sense of being British. That people think they have a nationality isn’t a belief; we know people think they have a nationality. We know thinking you’re British isn’t the same thing as liking to drink cups of tea, or another British stereotype. It’s exactly the same with gender identity. We know people have a sense of being male, female, etc. We know they have lots of different beliefs about why they have that sense. We know having that sense isn’t the same as liking pink, or any other stereotype.