Clearly the nomination is, and always has been politically motivated. As to whether it's racist, let's be daring and innovative, and consult dictionary definitions of "racist."
Merriam-Webster (online):
"having, reflecting, or fostering the belief that race (see RACE entry 1 sense 1a) is a fundamental determinant of human traits and capacities and that racial differences produce an inherent superiority of a particular race."
Dictionary.com:
"noun
a person who believes in racism, the doctrine that one's own racial group is superior or that a particular racial group is inferior to the others.
adjective
of or like racists or racism:
racist policies; racist attitudes."
Cambridge English Dictionary (online):
"someone who believes that their race makes them better, more intelligent, more moral, etc. than people of other races and who does or says unfair or harmful things as a result:
Two of the killers are known to be racists.
She cannot understand how her husband could be branded a racist.
racist
adjective disapproving
coming from or having the belief that people who belong to other races are not as good, intelligent, moral, etc. as people who belong to your own race :
He furiously denied being racist.
They were the victims of a vicious racist attack.
racist remarks."
Collins English dictionary (online):
"NOUN
1. a belief or doctrine that inherent differences among the various human races determine cultural or individual achievement, usually involving the idea that one's own race is superior and has the right to rule others
2. an overt policy, system of government, etc., based upon or fostering such a doctrine; discrimination
3. the maintenance of social, economic, and political structures that deny privileges and opportunities to members of certain racial groups
4. hatred or intolerance of another race or other races."
These definitions indicate that according to the most common usage, one is a racist if one believes members of a particular race, or one's own race, are better or superior to members of another race. I don't think it can be maintained, reasonably, that Biden or his administration want to nominate a black person based on the belief that black people are better or superior to white people. Is that what you maintain--the nomination is based on the belief the black race is superior to the white race?