The DNR (Do Not Resuscitate) is a doctor's order to not perform potentially life-saving efforts (CPR, cardiac shocks, ventilator, etc.) due to the unlikelihood of such efforts being successful in certain patients. This is meant to prevent suffering and respect the patient's wishes for his/her end-of-life care.
Usually, this order is put in place after a doctor's careful discussion with the patient or with the person who has POA for the patient regarding health care decisions (if the patient cannot give consent). The DNR order would usually be in place due to a terminal medical condition (advanced cancer) or elderly, frail patients with several medical conditions that make recovery difficult.
At times during COVID, these general guidelines were ignored, and these conversations did not take place before making patients DNR.
In April of 2020 the NY State Health Department issued new guidelines saying that patients found without a pulse at the scene of an accident should not be resuscitated. The longstanding policy before the pandemic was to try and resuscitate such patients for 20 minutes.
Perhaps because the policy was too wide too soon the EMT union and other first responders protested these changes and the decree was reversed after a few days.
The UK was not as fortunate, after an investigation by the Care Quality Commission looking into the use of DNACPR (do not attempt CPR) orders used during COVID it issued a report which found the following: 
DNACPR notices have been applied in a blanket fashion to some categories of person by some care providers, without any involvement of the individuals or their families.
Almost 10% of people using services or families said they had experienced pressure or use of DNACPR orders.
34% of people working in health and/or social care said they were under pressure to put DNACPRs in place without involving the person.
71% of advocacy organizations and campaigners said they experienced DNACPR orders put in place or pressure to make them without being involved in the decision.
The Joint Committee on Human Rights of House of Commons and House of Lords, found that "The blanket imposition of DNACPR notices without proper patient involvement is unlawful. The evidence suggests that the use of them in the context of the Covid-19 pandemic has been widespread."
Amnesty International issued a report documenting similar violations of the use of DNR policy in the UK.
Amnesty conducted several first-hand interviews with healthcare providers and others around the misuse of DNR orders, including one who explained “Discussions on advanced care planning should be warm and natural conversations. This is not how they should be done. One care home with 26 residents had 16 residents sign DNARs (do not attempt resuscitation) in a 24-hour period. It was distressing for staff and residents. . . . Care homes felt like they were being turned into hospices and being asked to prepare to manage deaths instead of managing life.” 
These abuses were known even as early as April 2020 when seven organizations representing the interests of the elderly signed a letter expressing outrage saying, "We are seeing shocking examples where blanket decisions seem to be being made about the care and treatment options that will be available to older and vulnerable people, who have felt pressurised into signing Do Not Attempt CPR forms." 
The Telegraph reported that children with learning disabilities like Down's Syndrome and Autism were asked to sign DNR orders even though they did not have a life-threatening illness. Parents were asked during routine 'heath checks' if they wanted to not revive their child if resuscitation was required. Upon being asked, one parent responded, "that's a disgusting question." 
One study showed that 89% of hospitalized patients that died with COVID had DNRs. The study concludes "In this cohort of patients with COVID, a DNR order was found to be a significant predictor of mortality, a finding that persisted after adjustment for other important clinical factors."
Another study looking into the factors that lead to hospitalization and death with COVID, found that "people with severe mental illness and learning disability had the highest odds of admission and death." It was a greater predicter that even age or weight.
In Canada, Dr. Nguyen told an inquest into elderly COVID deaths that many elderly Canadian patients actually died of euthanasia. While working in long term care centers, he found many obstacles in his way when he wanted to transfer a patient to the hospital. He also said the treatment protocols were end-of-life care and focused on the use of strong sedatives. It was his opinion that many elderly patients could have been saved with proper care.
Dr. Hebert, a professor at the University of Montreal in gerontology, used stronger words at the same inquest, saying, "these deaths represented a massacre by systematic ageism."
This is one example of how the panic of the pandemic, cowardice from the medical profession, and overreaching government bureaucracies trampled on patient rights during the pandemic and led to unnecessary deaths.
 Open letter from "Age UK"https://www.ageuk.org.uk/latest-press/articles/2020/04/age-uk-response-to-dnr-forms/