The evidence for this is pretty slim, at least so far. The patients sent to nursing homes were mostly those being released from hospitals, largely meaning people who were theoretically over the infection and likely no longer spreaders. (Getting a negative test after hospitalization for COVID was pretty much impossible back then, because there were too few tests available to retest known cases.)
The most recent numbers I’ve seen indicate about a third of New York’s COVID deaths occurred in long-term-care residents (ca. 15,000 out of 47,000). Compare and contrast with, for example, North Dakota, where about sixty percent of COVID deaths occurred in residents of nursing homes, assisted living, and other long-term care (874 of 1471), even though North Dakota certainly had the opportunity to learn from what happened in NY and did not have an analogous order sending COVID-positive people to nursing homes.
COVID is most deadly to the elderly with comorbidities, which is a pretty good description of your average nursing home resident anyway. Another problem with the “blame nursing home deaths on Cuomo” argument is the timeline: in New York, the death rate peaked in the middle of April 2020. However, the executive order sending recovering COVID patients to nursing homes wasn’t signed until March 25, and significant numbers of such patients weren’t actually received in LTC facilities until several weeks later (i.e., the middle of April). If those patients were actively spreading the disease, you’d expect hospitalizations to start going up in mid- to late-April and deaths rising a couple of weeks after that, but in fact the death toll was in free fall by the end of April.
The evidence suggests that most LTC patients were infected earlier, mostly in March, which suggests they were mostly infected too early to have been infected by returning COVID-positive patients and instead were infected by nursing home staff and visitors (visits weren’t shut down until March 12, e.g.).
That doesn’t justify hiding the numbers, of course, but does indicate the “he sent elderly people to die and kill other elderly” is a false narrative.