I'm not sure why I hadn't thought of this earlier as most my stories are basically Fantasy with a capital F so let me get right into it. What separates 'Fantasy' from 'Contemporary' works isn't just where it's set but also the level of contrivances that are allowed.
As I've said before, every story allows a certain level of contrived scenarios where Destiny and Fate are actually a thing. Fantasy stories in particular work best when you go all in on your imagination.
I know you all have had it drilled into your brains that a certain level of 'realism' is needed even in a fantasy story. However, what most mean by that isn't adding the laws of physics to your story but keeping it internally consistent with clear laws and limits.
I'm pretty sure you guys don't need a rundown in how society works because fantasy societies work the same way expect they have the word 'Magic' added to them. Do NOT rip off Elves and Dwarves from the Lord of the Rings and flex the creative muscles in your brain a little. There's no limit to the kind of magical races you can make in a Fantasy!
This also applies to magic. However, people only remember limitations more than what a persons using Magic System can generally do since 'magic is omnipotent unless proven otherwise'. There will be no narrative stakes or tension if you can't even make sure random nobodies aren't shooting off nukes and your main character isn't invincible beyond measure.
There are people who tend to overthink about how to write Fantasy since it's such a popular genre everyone and their dog is writing. You don't need someone else's guideline to write a Fantasy since most good Author's base them out of existing literature of the past or modern ones they are retelling using their own tropes and characters.
You'll never get anywhere if you need someone else to flex your creativity when looking into the past brings forth many mystical stories and myths that all wouldn't be possible without a little bit of magic sprinkled onto them. The classic LitRPG genre with stuff like Guilds and Adventures is popular to use nowadays but only because you don't have to explain much in a story that's so easy to figure out.
If you're going to use the LitRPG setting with dungeons and dragons, make sure you make it character driven and focus on people rather than explaining how fireballs work. The only reason Slime Reincarnation (That Time I Reincarnating As A Slime) or Sword Dad (I Was A Sword When I Reincarnated) are so popular is because behind the Power Fantasy are well-written and diverse characters.
If you want to write your own Fantasy World unique to only you, then it's best to start researching ways to ground it with your audience. These days people want to read about 'people' more than someone dumping lore about a fictional world they don't care about. Even pure Fantasy stories needs a protagonist that can be the reader's eyes and ears.
Now, thanks to the Isekai Boom, you may think that a main character HAS to be reincarnated for basically no reason whatsoever. However, that is ill-advised as people reincarnated for trivial reasons bore the audience to death. There's this Fantasy story about this non-reincarnated girl who was raised by Death himself in a regular medieval magic world, causing her to be a mix of creepy and cute all at the same time. This is an example of the kind of plots which are interesting BECAUSE their MC is a member of this world but special rather than some random guy from Earth who just so happens to be Isekai'd.
Isekai can be done right when the main character's rebirth or transportation into this world holds some sort of meaning. However, it can turn into a very boring story with maybe one or two gimmicks if you aren't even thinking of an ending for it.
Getting back to the main point: You seriously won't be able to write a Fantasy properly unless you at least know something about characters (If you haven't already figured that out already).
How the life of this character, under the special upbringing that only those of your Fantasy World go through, is interesting to the reader depends of where you take the tropes of your regular Fantasy.
You can go the 'Epic Fantasy' route, then copying the Hero's Journey is fine as long as you switch it up a bit. As long as you understand the fundamentals of a Hero's Journey and not look at it as the ONLY WAY TO TELL A STORY then you're on the right track.
Those who are wondering what a Hero's Journey is can find the link at the bottom. Also try searching for Dan Harmon's Story Circle for a more character driven version of it on YouTube. Anyway, this trope is basically the origin of the whole 'Chosen One' trope.
As for what I meant by Epic Fantasy, it is actually quite beloved type of story for many who love the Fantasy genre. It could be about the journey about a chosen one destined to defeat a Big Baddy like Eragon, Lord of the Rings, etc. There are even shorter and more simplified versions of this which is basically where the 'Hero Vs Demon King' trope came from. As long as there's a quest fraught with danger then people would love to read about a chosen one being able to win against their foes.
Another route you can take is Dark Fantasy, where all the lovely tales of HP Lovecraft comes from. His stories may lean more on the spectrum of supernatural tales about Dark Gods and Cults but the way everything seems to be ripped out of a nightmare is what I'm trying to focus on. If a regular Fantasy is like a dream then a Dark Fantasy is one you'd rather avoid since the world is screwed up.
And I don't mean the characters are screwed up or insane by any means, I literally mean either the Magic System or how society works is genuinely screwed up. Read 'Dungeon Seeker' as an example of this (Warning: Don't read it if you don't want to pollute your innocent mind with all the corruption in this story). Either way, it could be the Magic System relies on the blood of orphans, or it could be you have to kill a loved every time you cast a spell. The main point is that this Fantasy World is just hell.
Now, I could move on to Urban Fantasy and other sub-genres, but that would be wasting my time and yours since TV Tropes exists for a reason. Just remember what I've said and have a clear goal in beginning and end planned for your character's development and you'll be fine. There's nothing better than a story that's focused after all.
HelloFutureMe and others on YouTube such as OverlySarcasticProductions have more to say on this subject.