FP patterns for combining data from different sources (preferrably in Kotlin and Arrow)

Disclaimer upfront: Recently, my interest in functional programming has grown and I've been able to apply the most basic approaches (using pure functions as much as my knowledge and working environment permits) in my job. However, I'm still very inexperienced when it comes to more advanced techniques and I thought trying to learn some by asking a question on this site might be the right idea. I've stumbled over similar issues once every while, so I think there should be patterns in FP to deal with this type of problems.

Problem description

It boils down to the following. Suppose there is an API somewhere providing a list of all possible pets.

data class Pet(val name: String, val isFavorite: Boolean = false)

fun fetchAllPetsFromApi(): List<Pet> {
    // this would call a real API irl
    return listOf(Pet("Dog"), Pet("Cat"), Pet("Parrot"))
}

This API knows nothing about the "favorite" field and it shouldn't. It's not under my control. It's basically just returning a list of pets. Now I want to allow users to mark pets as their favorite. And I store this flag in a local database.

So after fetching all pets from the api, I have to set the favorite flag according to the persisted data.

class FavoriteRepository {
    fun petsWithUserFavoriteFlag(allPets: List<Pet>) {
        return allPets.map { it.copy(isFavorite = getFavoriteFlagFromDbFor(it) }
    }

    fun markPetAsFavorite(pet: Pet) {
        // persist to db ...
    }

    fun getFavoriteFlagFromDbFor(pet: Pet): Boolean {...}
}

For some reason, I think this code dealing with the problem of "fetch one part of the information from one data source, then merge it with some information from another" might benefit from the application of FP patterns, but I'm not really sure in which direction to look.

I've read some of the documentation of Arrow (great project btw :)) and am quite a Kotlin enthusiast, so answers utilizing this library would be very appreciated.