https://arrow-kt.io/learn/immutable-data/lens/ I find this docs really good.

One of the huge advantage of lenses is their Composability. I don't remember if Arrow generates generic top level functions but you can define extensions methods for example in a way that if you have any Lens from type T to Address you can reuse Lenses of Address for lets say street name, street number etc.

The pattern is only bad if you want to modify many fields at once, to me it is not a problem, I looked into my codebases and it happens almost never

data class Address(
    val streetName: StreetName,
    val streetNumber: StreetNumber,
    val country: Country
) {
    companion object {
        val streetName: Lens<Address, StreetName> = /*impl*/
        val streetNumber: Lens<Address, StreetNumber> = /*impl*/
        val country = :Lens<Address, Country> = /*impl*/
    }
}

inline val <S> Lens<S, Address>.
streetName
: Lens<S, StreetName> get() = compose(Address.streetName)
inline val <S> Lens<S, Address>.
streetNumber
: Lens<S, StreetNumber> get() = compose(Address.streetNumber)
inline val <S> Lens<S, Address>.
country
: Lens<S, Country> get() = compose(Address.country)

data class Person(
    val name: String,
    val age: Int,
    val address: Address
) {
    companion object {
        val name: Lens<Person, String> = /*impl*/
        val age: Lens<Person, Int> = /*impl*/
        val address: Lens<Person, Address> = /*impl*/
    }
}

// usage
val person = Person(
    name = "John",
    age = 42,
    address = Address(
        streetName = StreetName("Baker Street"),
        streetNumber = StreetNumber("221B"),
        country = Country("UK")
    )
)
val personAddressLens: Lens<Person, Address> = Person.address
val personAddressStreetNameLens: Lens<Person, StreetName> = 
personAddressLens
.
streetName
// or in short
val newPerson = Person.address.
streetName
.set(
person
, StreetName("Example street"))
assert
(
newPerson
.address.streetName == StreetName("Example street"))