There’s a typescript client here, you could look at that for examples, I can’t see any dedicated API documentation anywhere https://github.com/LemmyNet/lemmy-js-client/tree/main/src
See more details in this issue here https://github.com/LemmyNet/lemmy/issues/2937
Flippers wouldn’t help really given how horses actually swim, they kind of kick back with each of they’re legs in a sequence similar to a trot. Their hooves already have a bit of a hollow which likely helps with swimming. Honestly though horses are pretty good swimmers, because they have huge lungs which helps them stay afloat with ease