And yet it is still a very minority thing...
GRCs and legislation is merely sound on the wind - it doesn't change the immutable fact that you are born biologically male or female and can not change that. You can have legislation, you can have operations, you can change your name, and you can dress as you wish - you are still biologically male or female as you were born - any belief that anything else can take place is mere fantasy.
That is not to deny that there are those who have mixed feelings about how they identify - society has strong concepts of how a man / woman presents / looks / acts / etc. and it is easy to see that someone who is biologically one may feel more of an association with all the non-bilological elements that society says is the other - but that doesn't make them a different biological sex.
The issue that exists is how society boxes people up and defines them / puts boundaries around them - and absolutely we should allow people to express themselves as they wish - if they feel more 'male' or more 'female' then they can express themselves in that way, where society defines male and female as it does... There is no issue with dress or hair styles, colours, jewellery etc. all of which society uses as a shorthand to define male and female - but none of that changes whether they are a man or a woman underneath - that is biology, it is chromosome based and can't be changed
For clarity we should absolutely separate our understanding that sex is defined biologically and makes you a man or a woman - from the concept of gender or expression where there should be no issue. The problem is that the two are conflated where one is physical and real and the other is internal, expression and feeling. You can change the latter, you can not change the former.
So a gender recognition certificate ultimately should have zero purpose - we should have a society where we have no issue if a chap wishes to wear a skirt to school / work, we should not be bothered if a girl wants to do woodwork and a boy likes to do knitting - all of that is gender stereotyping which should be removed - but it doesn't matter what people want to do, or legislate for there is no human out there who actually has the skills to turn a physical man into a physical woman or vice versa - we are not God, even after surgery it is all about presentation, biologically that person still remains as they were born...
so we need to separate our understanding of language to split these two things - that is why it is important that boy / man is someone born male, and girl / woman is someone born female - however much anyone wishes to that can not be changed - so changing wording in a dictionary simply is an inaccuracy.
More accurate definitions might be:
Man - someone born biologically as a man with male hormones and male physical characteristics
Woman - someone born biologically as a woman with female hormones and female physical characteristics
Transwoman - someone born male, who remains biologically male but wishes to present as a woman and conform to societal stereotypes of woman - may have physical surgery to look more 'female' but still remains male biologically.
Transman - someone born female, who remains biologically female but wishes to present as a man and conform to societal stereotypes of man - may have physical surgery to look more 'male' but still remains female biologically.
It isn't complicated - so you have to ask why is it being made complicated - and the only answer can be because there is an additional parallel agenda - so we should fight that, and dictionaries are clearly a part of this fight because they appear to define language. In fact, they can't change something over which they have no control (biology) and however the language is changed the biology will remain the same - changing the definition of a word doesn't suddenly mean that someone's hormones change ;) so we need to say that it is important to not pander to trends which have no basis in fact, but to maintain accuracy.