“One of the main groups that humans can be divided into according to their physical differences, for example the colour of their skin.” oxfordlearnersdictionaries.
I have a lot of issues with the above definition.
There are no two human beings who are physically identical. Moreover, two true twins may even appear different by having a different skin colour, hair colour etc. Furthermore, what is common between the physicality of people far outweighs their differences. Ask a sincere biologist if in doubt !

Race in the Cambridge dictionary is as follows though:
“The idea that people can be divided into different groups based on physical characteristics that they are perceived to share such as skin colour, eye shape, etc.” .

So after all, it is but an idea. It has no real substance.
Race is a disturbing word. Maybe, it is a cover for an illness. It even clashes with the English language and culture.

For
“Beauty is only skin deep!”
and
“Don’t judge a book by its cover !”