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.
Yes, we know this.
However, the women who have won their cases for been bullied, harassed, victimised, discriminated against, forced out of their jobs, and then continued to be victimised by their former employers after leaving didn't do the things in your example.
I don't know if you followed any of the tribunals or read any of the judgments, but in those cases it is those on the opposite side of GC, those with 'gender identity beliefs' that are being discriminatory. Them acting on their beliefs has led to women being harassed and sacked (unlawfully) and winning pay-outs for discrimination.
Employers do need to be very careful indeed...