ehhh....
You have genes. Certain genes are well adapted to certain environments, for example hi/low melanin to protect from UV radiation. In environments where people don't move a lot, such as the Earth 5000 years ago, genes will tend to cluster together, and if you have someone's genetic makeup you can make informed guesses about their phenotype.
The problem, imo with 'races' is that the modern world has created too many hybrids to be able to accurately guess much information about someone's genetic makeup from their phenotype.
Blue eyes for example, which maybe 5000 years ago were only found in one small corner of the globe, are common in many different places, and associated with many other types of genes. You can no longer reliably predict that someone with blue eyes will have blonde hair for example. Or that they won't also have say sickle cell anemia when in the past those two traits were probably never found in the same person.
Like for example when in the US someone marks their race as "Black" in some census form, that tells you almost nothing besides maybe that they likely have elevated levels of skin pigmentation.
You have some genetic clusters, such as those found in the Kenyan Rift Valley, where they have good genes for long distance running, and others, such as those found in Jamacia and West Africa, better suited for explosive sprinting. Both of which tend to be associated with high levels of skin pigmentation.
Operating at the level of 'races', which, from what I can tell, basically means 'skin color', completely misses this sort of detail, and is, in my opinion, a mental model that is so crude, and so lacking in granularity as to be basically worthless.
Genes exist. Races... if you're using that term to mean "certain groupings of genes which are often found together, usually in groups of people that have spent a long time living together in the same environment", then yes, they exist, but then you have many people that you'd not be able to fit into a 'race' - basically every stereotypical American who is "one eighth Irish, one eighth Italian, one eighth Swedish, one eighth Chinese...." is going to have a set of genes that is not associated with any "race".