This idea of Greenland being isolated for centuries while it was still widely believed in Denmark that Norse people lived there is one that I always found puzzling.
Where are you getting the idea from that it was 'widely believed' Scandinavians were still living there?
The last record of contacts with the Greenland colony was in 1410, and the colony is likely to have failed in that decade (Nedkvitne, Norse Greenland, 2019). By the 1470s, the Danish king Christian I sent the German sailors/privateers Hans Pothorst and Didrik Pining to go there and possibly to explore the northern islands further. The details are sketchy and that void has given rise to some rather wild speculation they made it to Newfoundland or Labrador. That's not so likely but it's generally considered they did make it to Greenland (which is attested for instance in Olaus Magnus account in the 1500s), which would be the first visit since the colony failed.
By 1521, Christian II had plans for a military expedition to retake Garðar, the diocese of Greenland, from 'the pagans'. In preparation, the pope had issued a bull naming a new bishop of Greenland two years earlier. However, the events that lead to the dissolution of the Kalmar Union and ultimately the deposition of Christian got in the way. So that voyage never happened.
As said, Olaus Magnus' 1555 work on the History of the Northern Peoples has several chapters on Greenland, it mentions the inuit and their leather boats (which he recorded having seen several himself displayed as trophies at the cathedral in Oslo). As said he also mentions Pothorst and Pining being there, and engaging in piracy. He claims they installed a compass-rose marker on the island of Hvitsark between Greenland and Iceland, and depicts it in his book and on his earlier Carta Marina, top left (1439). But Olaus Magnus does not speak of any Scandinavian presence there, which he surely would have if he thought there was any.
Around the time Pothorst and Pining were on their first expedition, In 1476, Nicholaus de Dacia in Poland was writing that "To this island [Greenland] the Pygmies recently came sailing and after having expelled and killed the Christians, they took possession of the country" (British Library MS Sloane 1680, f93v)
Contacts with Greenland had become very sporadic towards the last decades of the colony. After the last bishop of Garðar had died in 1378, they didn't bother appointing a new one. (although a German bishop of Iceland, who'd never been to Iceland, attempted to have one appointed in 1448. Nedkvitne suspects this was just a ploy by a corrupt bishop to sell the position)