"Republican candidate, Glenn Youngkin, was able to entice moderate suburban Republicans to believe that with him it was safe for them to return to their Republican roots."

I doubt many people switched sides. More likely the D's lost some of their soft support. These voters were not motivated to make the trip to the polls.

Too many Medium political writers fail to recognize the importance of soft support. Negative advertising convinces the soft support of the other side not to vote. But they did not switch their preference.

https://medium.com/tiered-democratic-governance/negative-political-advertising-1ab0e2d214d8

I just Wiki'd the race results:

https://en.wikipedia.org/wiki/2021_Virginia_gubernatorial_election#Results_3

Youngkind (R): 1,659,000

McAulife (D): 1,580,00 the difference is 79,000 votes

Other: 25,000

Didn't vote: 2.688.000

It's not hard to imagine at least 79,000 soft D supporters are tucked into that "didn't vote" category.