Epistemological Tunnel Vision Fallacy:
When someone thinks that there is only one possible epistemological method, and when that method is debunked, they land on epistemic nihilism – thinking that there is no reliable truth on the matter. Their fallacy rests on the assumption that there was only one method to begin with. They fail to see that there are other tunnels, or epistemological methods for getting to the truth.
For example, covid testing – the cheap, publicly available tests are unreliable (frequently inaccurate with both type 1 and type 2 errors [false positives/false negatives]). So, someone with epistemological tunnel vision will assume that the publicly available cheap test is the ONLY way to verify that covid, as a general phenomenon, exists. Because of the inaccuracy of the publicly available test, they will lose confidence in the evidence for covid's existence. They will then commit the fallacy of thinking that covid is not real, failing to realize that there are other epistemological methods (like expensive labs) for proving that covid exists.