It should be noted - this definition as genocide as destruction of a culture (instead of physical murder of a people) also supports the idea of "white genocide":
A targeted effort by people with power to liquidate white peoples' group identity ("abolish whiteness") and to marginalize and obscure their traditional cultural touchstones ("don't teach books by dead white men" and related efforts to avoid teaching Shakespeare, the Bible, old white philosophers, etc), efforts to bring in many immigrants to make whites minorities in areas where they were previously a majority (and gleeful anticipation of this outcome), etc.
This definition does seem to mean something. E.g. I'd say Uighurs and Tibetans are undergoing genocide by China, even though China isn't running death camps. China has the intent of erasing these groups as groups and is systematically working towards that goal.
And it has been used this way extensively. People talk about "genocide" of trans people in America. Or the "genocide" of Native Americans, who, although they were almost wiped out by disease, and were then abused in horrid ways, were never the target of a campaign of physical total murder. Reservations are terrible, but they're not Treblinka.
On the other hand, the definition seems incoherent. Is it possible for blacks and whites to both be undergoing genocide right now? I suppose so; maybe it's a war with each tribe trying to dissolve the other.
I suppose you could look at intent as the difference as well: Are people trying to abolish blacks as a group? Is this the goal, or a side-effect? Are people trying to abolish whites as a group?
Does it require a chance of success? Is the intent to liquidate white culture enough to call it genocidal, or does it actually need to be actualized with a strong chance of success? How much chance?
Or does it only require an effect? Is the effect of liquidating black culture enough to call it genocidal, even if it's just an incidental side-effect, or does it need to be an intent? When we bring modern music and food to an isolated tribe, thus displacing their traditional music and cuisine, is that genocide? Because we just destroyed their culture forever.
Things get fuzzier because the academics in power at the moment - all leftists - want to be able to use this word to describe actions against people they like, but not against those they dislike. Hence the bobbing and weaving between definitions: When it's against whites, genocide means gas chambers only. When it's against blacks, it means a lot of young criminals spending time in prison.
I think it would be better to narrow the usage of this word. If people are trying to liquidate another culture, let's figure out another word for that (and please not "cultural genocide").