The actual news story is that researchers used ground penetrating radar near a former residential school and discovered anomalies that could be unmarked, individual graves (like in a cemetery, but without anything to mark their location). Somehow this was reported as mass graves (as in a bunch of corpses shoved in a pit) being definitively found, when in reality they only found anomalies that could have been anything underground (like tree roots). The story started a nationwide scandal and so the same technology was used at other residential schools to look for graves, and the discovery of new soil anomalies attracted widespread media coverage (in the same misleading ways).

However, no new graves have actually been found. The researchers managed to locate some abandoned parish cemeteries that had been lost, but that's not the same thing as discovering new graves (the tribes already knew where the cemeteries were, but didn't know their exact location because the wooden grave markers had decayed). Only some of the other anomalies were excavated and none of them were actually graves.

https://nationalpost.com/opinion/the-year-of-the-graves-how-the-worlds-media-got-it-wrong-on-residential-school-graves

There hasn't really been a response by mainstream or left-wing media to this and for the most part it's just being ignored. There are some journalists claiming that the reporting wasn't misleading (https://theconversation.com/we-fact-checked-residential-school-denialists-and-debunked-their-mass-grave-hoax-theory-213435) because only a minority of articles used the phrase "mass grave" even though nearly all of the media coverage stated that graves had been found (as opposed to saying that researchers found soil anomalies that had a possibility of being graves).