There's no such thing as a racial marker - race is completely arbitrary. That's why you occasionally get cases of people pretending to be black, because "being black" is a fluid category and as such people who are white fakers can look very similar to people who are black but light-skinned.
Race isn't completely arbitrary. It's basic evolutionary theory. Living in different places develops different features. These features helped survival in one way or another and became typical for certain areas. A native of Japan does not look like a native of Uganda. That's the hard, physical reality. Though of course many people are hard to place in one race or another.
The following comparison may sound offensive. Apologies if so.
Different dog breeds are a thing. Very obviously. Crossing breeds will produce a mongrel who is hard to categorise. That does not mean dog breeds are completely arbitrary. Of course, human variation is more complex than that of dogs, considering we don't have kennel clubs to impose certain ideals, but the principal is the same.
Here's another argument: Just because there are blurred lines between races does not mean races do not exist.
Also, trans and enby people are ingrained throughout all of human history, where as race as a distinct idea was gradually invented starting around the late 1600s taking their first step into ideas of biology.
The idea wasn't invented in the late 1600s. It began to be explored in a scientific manner at that time. Something doesn't need a modern intellectual framework to exist. For instance, did the world explode into roundness as Galileo/Ptolemy began spreading their ideas? No. Sailors knew just by observing the curvature of the earth, but Galileo in particular helped develop a scholarly discussion surrounding it.
Likewise, before racial science began down its largely-misguided path, the medieval world explored concepts of race. Usually in an equally misguided way - namely by portraying them as monsters. Mongols, Jews and black people were all discussed and categorised as distinct races.
Before this, the Ancient Greeks had a fairly decent concept of race. They believed that it was tied to the environment.
I think one of the main things to consider is that race didn't matter as much in the more distant past. You lived in your polis, village, town, tepee, hut and interacted with foreigners only rarely. When you DID interact with other races, it was like Xenophon meeting the Carduchians in the retreat of the Ten Thousand - they were "a fierce, war-loving race, who had never been conquered. Once the Great King had sent into their country an army of 120,000 men, to subdue them, but of all that great host not one had ever seen his home again."
Even were the ancients completely ignorant of race - which they obviously are not - that's no reason to assume that it does not exist. We understand selection and the formation of races in a way which was impossible at their time. They saw races, named them monsters, and that was all.
We see races. Understand how the environment led to certain mutations and differences. Then we categorise.
And boy do we categorise badly, with generalisations galore. But at least we know there is SOMETHING there to categorise in the first place.
And, of course, underneath these physical differences people are still people. Which means that those who claim to be a different race are trying to appropriate the cultural ramifications of being that type. In the highlighted cases this seems to be because they want to seem/be more "woke."
Similarly, transgender people are just people. The difference between male and female, despite physical differences, is minimal. What is desired is to be treated a certain way. Someone whose sex is male wants to be treated like someone whose sex is female. Hence dressing in certain ways, walking and acting certain ways, having surgery and taking medication to prevent beard growth. (Actually not sure about that last, but I think that's part of the process?)
To sum up, I guess:
Race is physical. But it has cultural implications which some wish to appropriate.
Sex is physical. But it has cultural implications which some wish to appropriate.
So, to ask my question again, why say that transgender-ism is a thing but transracial-ism is obviously something to be ridiculed? Both seem to be exactly the same to me, just applied to different physical attributes.