Most people in the known realm are probably human, though there hasn't exactly been a census. I remember hearing there's anywhere from over a hundred to a few thousand intelligent species (again, no overall census, and it's really hard to determine how to count spirits). We're uncertain why - going theories are that humans are unusually common in the multiverse, that the realm is inordinately fond of stealing humans, and that dimensions with humans are clustered in such a way that they appear nearby each other in the realm, so if we went far enough away from our islands we'd run into sections with very few or no humans.
There's a few noticeable groups of species too - elves are generally taller than humans, with pointed ears, better hearing and eyesight, and significantly longer lifespans (there's at least ten species of elves I think?), while dwarves are shorter and stouter than humans, with less sexual dimorphism, better eyesight (especially in the dark), and slightly longer lifespans (not sure how many species of dwarves, there's a couple though). (There's similarities beyond those, but I'm not a biologist). My home continent also has a few dragons, as do a few other reality-islands, though dragons species vary really widely and the 'dragon' category is I think poorly defined
There's also spirits - that's a really broad catch-all, but most spirits are either animal spirits or landscape spirits. Like, I'm friends with a cat-spirit, and I know a desert-spirit from my university days, plus I've met a few river-spirits. Spirits are magically powerful, usually shapeshifters, and capable of talking in any language.
There's the Akest, they're pretty common where I grew up. They're reptilian and single gender, as are most of the big creatures from their home dimensions.
The island-continent of Omaven has a ton of different species, too. I'm really only familiar with the Incusai (had a blue group one as a roommate in uni), they're small winged humanoids whose skin, hair, and wing color determines their gender. They're green up through puberty, when they start choosing which of three color-groups to be in (purple/pink for male-ish, white/cream/grey for female-ish, and blues for the third gender), though some choose to stay green I think?
I heard about intelligent trees once. Not, like, tree-spirits, but an actual sentient tree. I'm not sure if that was a tall tale or not.
There's also some animals we used to consider non-sapient, like Shras sand-serpents, crows, parrots, elephants, and dolphins. (There's debate over whether similar animals in the human source worlds were also sapient, or if the animals in this realm come from a different evolutionary path). Some people can magically talk to plants, non-language animals, or inanimate objects, there's debate over whether that's proof of sapience
There's the occasional intelligent artifact, they're usually made with magic instead of occurring naturally. A captain I know has a talking ship, and there's been some debate over how much we can improve the systems on our ships before they count as people