Is Google impacting elections on a “massive scale” by sending manipulative “ephemeral experiences” as a researcher has claimed, or is that not happening, or at most, an exaggeration?

That phenomenon alone is not a powerful influencer but a significant one. The basic answer to your question is that there is significant manipulation taking place via Google and what it does to the minds of those using its services, but that involves a number of manipulations, not solely the one described by the source you mention. There are many ways Google stacks the decks to favor the Democratic Party and its doings and the liberal ideology of the left, in many respects, about many issues of the day. It is being done because they are manipulated to do it; they are manipulated to believe it is worth doing and important for them to do so; they are made to feel patriotic in fact, even as they are robbing the nation of democracy through individual rights and privileges of participation in society. Being able to vote for a candidate of one's choice is a simple pragmatic act of individuality, under ideal conditions, but so is the ability to think a thought, to have a political preference concerning an idea or a representative of a political group and the ideology they represent, and so on. When ideas themselves and, even more fundamental, the inner beliefs of a person are being manipulated through a series of maneuvers to bring propaganda messages to bear in influencing their thinking, this is going far beyond providing a communication gateway and platform. In effect, it is serving up a tainted meal through its offerings, because they may be shaped and sorted in ways to convey particular meanings, and to have a restricted reach to discourage certain ways of thinking and encourage others. That is the essence of mind control and is not only illegal but morally repugnant and a severe karmic misstep that will incur punishment at some point, because wrongdoing is wrongdoing regardless of the consequences, whether small or large.