Can someone answer a nagging question i have about CRT?

Edit: this question has been answered now. Thank you to everyone who took the time to help me understand.

the premise that race is not a natural, biologically grounded feature of physically distinct subgroups of human beings but a socially constructed (culturally invented) category that is used to oppress and exploit people of colour.

Okay… But we can take a DNA test and get our ancestry, telling us what percentage of what races make up our overall ethnicity. So how is race a social construct and not a biological feature, when we have a scientific method to determine our race? This part of the philosophy has been bothering me ever since I read it, and I’ve been hesitant to ask because of how offensive people get when you question this system.