Dear Hayder Gebreen , seems as if this relation is particularly being discussed for fiction stemming from India and the Middle East. Here are some articles you might find interesting:
https://ricerca.uniba.it/retrieve/handle/11586/352265/558138/5.Monaco.pdf
https://books.google.de/books?hl=de&lr=&id=RE2XCgAAQBAJ&oi=fnd&pg=PP1&dq=high+fantasy+and+postcolonial&ots=y8CQ0I2RHF&sig=LbwotuLiI0fxQiNZl40Gdvz-JfQ&redir_esc=y#v=onepage&q=high%20fantasy%20and%20postcolonial&f=false
Thesis Oriental Fantasy: A postcolonial discourse analysis of Weste...
I don't think they are related because postcolonial literature bears the primary setting, the earth and it is realistic while high fantasy bears a secondary setting, that is someplace out of the earth and it is highly romantic.
These could be indirectly related in the following sense: fantastic narratives could incorporate colonial/postcolonial characteristics. For instance, Avatar is a fantastic fiction which exposes the opposition between the colonizers and the colonized via an allegorical setting and structure. Many works of fantasy could be interpreted in the same manner, as allegorical post/colonial narratives.
Fantasy can also be called a kind of postcolonial literature, but in countries that were colonized
The context of this literature must be examined
Fantasy is linked to colonial literature not post-colonial literature. Much of the literature that depicted the Orient is based on fantasy much of it depends on tours of the mind. To cite one among hundreds of examples, in Vathek, William Beckford who is, later cited as a pioneer Orientalist, created a whole world entirely produced by figments of wild imagination.
Please see my:
Article William Beckford's Vathek A Call for Reassessment
Both share one thing in common; disillusionment. High fantasy presents ideal fantastic setting and in post colonial literature, readers discover that such ideal society promised to them is never realistic
Some time back I befriended a manual laborer in Nigeria in a writing group on facebook. We sort of instantly took a liking to each other. After a while he sent me manuscript of a fantasy novel he had written. It was not like he presented this straight away, and I sort of had to lobby him to get it. I saw that the story was well composed, even if there were huge syntax problems and other issues relating to his diction. I tried getting a publisher for him to fix it, but eventually realized that the only one stupid enough to do this much work for free was me. So, I spent a year editing the text (not full time). Of course, I then knew the exact problems with his syntax and how these related to his native tongue which was Igbo and sometimes pidgin. In the end I managed to get the text into shape, and published it for him at amazon. It is an entertaining novel, full of imaginary creatures, and it has plenty of action. I know nothing about the genre beyond Tolkien, only a few names. Still there is some subtext dealing with corruption in the fantasy novel, and I also noticed that this was an issue about which he had many opinions, none of them extreme, it just annoyed him. Here is the novel I edited: Flames, by Ify Iroakazi. It is one very few African fantasy novels I know. Even if Ify was a manual laborer when I met him, his family are all educated, and Ify later started university himself. (If you widen the concept of fantasy, what about Salman Rushdie?) https://www.amazon.com/Flames-Ify-Iroakazi/dp/B08JDTP9GB/
Always keep an eye on the roots of post-colonialism and the 'writing back' process and its function highlighted by Bill Ashcroft et al in 'The Empire Writes Back'. High fantasy is often about quests, overcoming problems, and crusades that can be both about resolving private and public problems or adjusting to difficult circumstances. These all have direct links to post-colonial / post-modern writing because of its intention to highlight inequality and either suggest ways of achieving resolution or concentrate on pointing out its damaging effects.
I really wanted to respond to this question. My thesis on Derek Walcott's 'Omeros' is published here on ResearchGate under the title 'Epic and Multicultural Aspects: the structure of Omeros'. At times my study explores the interface between the fantastic and the actual struggle to create a postcolonial epic for the indigenous people of the Caribbean. The fisherman Achilles' psychic journey back to his roots in Africa is presented by the poet as both a dream-like journey stimulated by sun stroke when Achilles is fishing with a mate in the Atlantic Ocean and the most vital transformation in the character of Achilles. The fantastic voyage on the wings of the sea swift is as real to Achilles afterwards as his conflict with his estranged lover Helen.
The danger in the question is to be prejudiced or limited in our view of fantasy. Achilles re-discovery of African roots can only happen in a transmogrifying, psychological/ mystical way. He can't go back centuries and revisit his father and his pre-colonial community 1000s miles away. But for this poor fisherman the return passage is more potent and real than as if he was a globe trotting jet-setter which financial freedom to visit anywhere. Some truths are best conveyed (perhaps only can be conveyed at times) through a fantastic metaphor like Achilles' flying back to his origins on the wings of a sea bird. The inner-experience of reclaiming his homeland helps his character gain a depth or understanding and empathy which enables a reconnecting with Helen, who perhaps is the personification the subject Island, St Lusia.
Walcott begins his epic with the personification of the trees 'cedars' critical in creating the canoes which sustain the livelihood of the indigenous fishermen. Personification can easily be construed under the term 'fantasy' but Walcott is pointing to the utter importance of these trees in the survival of the islanders, before colonisation. He naturally uses the fanciful to hark back to a pre-invasion time when 'The first god was the gommier. ' [Omeros, p.5] In a modern context the reader has to imagine/ picture/ fantasise the trees are important as supernatural beings who are all but worship. Yet Walcott appears to want the reader to move beyond this prehistoric view of nature to the modern world, but the poet sees the need to reclaim and understand the treasures of the past as relevant in the attempt to find new vision beyond the distractions and terrors of colonialism.
Another aspect of this interface between fantasy and actuality is how a range of mythological characters and events can be employed in the text to symbolise the heroic efforts necessary in overcoming the lingering legacy of European exploitation of the island and dominance of the sugar industry. This mythology or story-telling is a real as how to cure a wound which defeats modern medicine.
Philoctete's chronic injury has to be healed by Ma Kilman's obeah skills that have their origins in the earliest legends of the islands. Walcott again and again implies that we have to imagine and reclaim the most distant realities of ancient times which the poem's title Omeros, Homer also suggests, to create a new identity beyond the distortions of oppressive colonial rule.
The author valorises the past images in attempt to inspire the present residents to find the courage to realise a life that's postcolonial. But Walcott acknowledges that the way back can be as painful as the lunging and being driven into future.
The interface between fantasy and postcolonial literature can be understood if we approach fantasy as another form of reality, a secret but powerful inner-force, that is significant in shaping the new nation that somehow has to emerge from the shadows of colonialism, both for colonised and the coloniser.
Their relationship could be that they are all narratives, has imaginary settings, character & characterization, plot and and other elements of narratives. They portrays the culture of the people who are using them and an avenue of transmitting acceptable norms and values . They are tools which the narrator uses to lure the reader to see the world the way he sees it. Majorly they are usually done for language impartment since the language is only viable vehicle to convey literature of which they are part of.
It's worth looking at the work of Nalo Hopkinson to see how this can be done in practice by writers of fiction.