I have often referred to the 'Distortion Theory' as an explanation for cryptids such as the British Bigfoot, UFOs and their crew and other Fortean creatures. The basic premise is that an "intelligent other' interacts with humanity for its own ends, however it will not reveal its true nature but rather 'disguises' itself according to the era in which us humans witness it. This is the work of Spanish Ufologist Jose Caravaca and his main body of work is written in his native tongue, however there are now English translations becoming available. here is one such article:
"The paranormal component is a drift, perhaps the most important one, caused by the involvement of the human psyche in the decoding of this expanded reality accessed by the witnesses during the fleeting contact with an undetermined external agent, which may ultimately be the instigator, detonator or enhancer of these visionary episodes (not hallucinatory or imaginary)."
The full article is here:
https://ufoconjectures.blogspot.com/2023/01/an-explication-of-distortion-theory-in.html