According to an article by Nicole Wetsman and published in The Verge web site:

"Consumer genetics and genealogy company Ancestry announced a new feature, called SideView, that will give customers information about which bits of their DNA — and which parts of their ethnicity — were inherited from each parent. The tool can do that without having genetic information from the parents, which Ancestry says is a first in the industry."

"Genetic information is packaged in pairs of chromosomes, and each parent contributes one copy of most chromosomes. DNA analysis, though, reads the sequence of genetic information without sorting out which half different sections came from. Usually, the best way to sort that out is by comparing sections to the DNA of one or both parents. But Ancestry developed a technique that uses the company’s large DNA database — which includes 20 million people’s genetic information — to find overlaps between each user and cousins or distant relatives also in the system. It uses those overlaps to sort each section of DNA by which parent it was inherited from."

The article also cautions:

"The database, though, is largely made up of people with European ancestry — the feature is less accurate for users who have other ancestry from other parts of the world, according to a scientific article from Ancestry describing the technique. The paper has not yet been peer-reviewed or published in a scientific journal. Blind spots around people of color are a longstanding bias in genetic databases and genetic research more generally. DNA tests like Ancestry’s that tie your genetics back to a particular ethnicity are also often criticized for giving people an incomplete picture of what genetic heritage actually means and conflating ancestry with race."

Also:

"Ancestry can have 95 percent precision for 90 percent of customers."

You can read more at: https://www.theverge.com/2022/4/13/23021782/ancestry-dna-sort-genes-parents-ethnicity.