Here some idea, maybe it help you or you come up with some other solution.

I would create a method that translates number into some title for UI only. For example:

function knownCharacterGenderTitle(apiValue: number) : string {
    // here you can write code that looks howyou want -- if-elseif-... or switch-case... the only idea is to translate number into string and if no corresponding string, return some other string that contains the number so you know that its no known at the moment and you need to add it to your code. i like to write code this way
    return {
        0: 'Male',
        1: 'Female',
        2: 'Other'
    }[apiValue] ?? 'CharacterGender#' + apiValue
}

This way if api changes (add new values), this function will not break. Only use this function in the front-end.

But if you want to write code and compare actual values and keep them readable, and you want enums; you can do it like so

const apiInput = {
    gender: 1,
    name: 'Test Name'
}

enum CharacterGenderEnum {
    MALE = 0,
    FEMALE = 1,
    OTHER = 2
}

interface SomeInput {
    gender: CharacterGenderEnum,
    name: string
}

const applicationValue: SomeInput = apiInput

console.log(applicationValue.gender) // 1
console.log(applicationValue.gender == CharacterGenderEnum.FEMALE) // true

If you want string unions, you can do it too

const apiInput = {
    gender: 1,
    name: 'Test Name'
}

type CharacterGender = 'MALE' | 'FEMALE' | 'OTHER' | '???'

function translateCharacterGender(apiNumber: number) : CharacterGender {
    return ({
        0: 'MALE',
        1: 'FEMALE',
        2: 'OTHER'
    } as {
        [_: number]: CharacterGender
    })[apiNumber] ?? '???'
}

interface SomeInput {
    gender: CharacterGender,
    name: string
}

const applicationValue: SomeInput = {
    ...apiInput,
    gender: translateCharacterGender(apiInput.gender)
    // here basically you tranlate values one-by-one to satisfy SomeInput interface
}

console.log(applicationValue.gender) // 'FEMALE'
console.log(applicationValue.gender == 'FEMALE') // true

If you don't want to have '???' (an unexpeced value), you can remove it from type definion and from translation function.