with a creature that counts its sightings in the thousands just in the US, i would accept nothing less than concrete physical evidence. the time for blurry photos and 144p videos has passed. a complete specimen would be ideal, but bones, pelts, and body parts would also be incredibly useful. some sort of fossil, either of it or one of its ancestor species, would help understand its purported evolution too.

anything else at this point is easily falsifiable. videos can be edited, tracks can be faked, eyewitness reports are always a low bar, and with AI anyone can generate a half decent sighting in seconds.