"I can only presume you haven't read the link I posted"

Which link? You provide many and I usually read them.

"I hope you know I have more intellectual integrity than that."

I do and apologize for that.

"You seem to be assigning intrinsic value to the fact that we look at each other and make assumptions, even when those assumptions are wrong, and are then using those assumptions to conclude that racial categories are meaningful despite all scientific evidence to the contrary."

I assign no intrinsic value to it. As I go through my day the race or gender of the people that I interact with is unimportant to me, but it might be to them. Do people sometimes draw incorrect conclusions about the things they observe? Of course. I might be fuller of doubt about many things than most people, but it doesn't mean I should not think or form opinions about things.

If science (the most abused word in all of discussion) concludes that there are not observable dominant physical characteristics to commonly found in subsets of humanity known as race, the science is probably political science, an ever-changing set of opinions which conform to public opinion. At that point it is quibbling about evolving definitions of words. 𝐀𝐥𝐥 𝐨𝐟 𝐭𝐡𝐞 𝐭𝐡𝐢𝐧𝐠𝐬 𝐚𝐬𝐬𝐨𝐜𝐢𝐚𝐭𝐞𝐝 𝐰𝐢𝐭𝐡 𝐫𝐚𝐜𝐞 𝐟𝐚𝐥𝐥 𝐮𝐧𝐝𝐞𝐫 𝐨𝐯𝐞𝐫𝐥𝐚𝐩𝐩𝐢𝐧𝐠 𝐝𝐢𝐬𝐭𝐫𝐢𝐛𝐮𝐭𝐢𝐨𝐧 𝐜𝐮𝐫𝐯𝐞𝐬 𝐚𝐬𝐬𝐨𝐜𝐢𝐚𝐭𝐞𝐝 𝐰𝐢𝐭𝐡 𝐯𝐚𝐫𝐢𝐨𝐮𝐬 𝐠𝐫𝐨𝐮𝐩 𝐜𝐡𝐚𝐫𝐚𝐜𝐭𝐞𝐫𝐢𝐬𝐭𝐢𝐜𝐬 𝐰𝐢𝐭𝐡 𝐯𝐚𝐫𝐢𝐨𝐮𝐬 𝐬𝐭𝐚𝐧𝐝𝐚𝐫𝐝 𝐝𝐞𝐯𝐢𝐚𝐭𝐢𝐨𝐧𝐬. Thanks to intermixing an increasing number of people fall into the overlap and become less classifiable. People categorize, an ancient survival instinct.

"how many races are there?" & "definition of race, and an enormously more nuanced one that considers a wide array of genetic differentiation beyond skin tone (and would therefore lead to many, many more than five)"

It depends upon which characteristics you use to make the determination. I've continuously stated that I see it as something more numerous than skin color which is an analog ranging from dark black thru shades of g̶r̶a̶y̶ brown to very white. To attempt absolute boundaries might reduce it to three (white, brown and black). Native American and Hispanic are more political than physical distinctions.

If the only thing you could see about my wife was the color of her skin, you could draw no conclusion about a racial category other than brown which is not the characteristic that jumps out at people first or leads to the one she associates with.

All those words to say that we are not thinking of the same things. Perhaps I should choose a less offensive word than race for the dominant physical characteristics of subsets of humanity which are not limited to skin color. With apologies to Forrest Gump, "That's all I have to say about that."