I recommend having your "fetchWeatherForecast" function return an object with those methods available for parsing:

import { weatherAPIConfig } from "../weatherAPIConfig"

export async function fetchWeatherForecast(cityName) {
    let URL = `https://api.openweathermap.org/data/2.5/weather?q=${cityName}&units=metric&appid=${weatherAPIConfig.key}`
    try {
    const weatherForecast = await fetch(URL) //changed cuz I don't recommend naming your variable the same as the function
    const weatherForecastJSON = await fetchWeatherForecast.json()
    } catch (error) {
        console.log("Could not find given city");
        return "Could not find given city"
    }

    function getWeatherDescription() {
        return weatherForecastJSON.weather[0].description;
    }

    function getWeatherTemperature() {
        return weatherForecastJSON.main.temp
    }

    function getWeatherWindSpeed() {
        return weatherForecastJSON.wind.speed;
    }

    function getWeatherHumidity() {
        return weatherForecastJSON.main.humidity
    }

    return {getWeatherDescription, getWeatherTemperature, getWeatherWindSpeed, getWeatherHumidity}
}

So now in your "Row.js", you can do:

import React from 'react'
import {fetchWeatherForecast}  from '../../functions/fetchData'
import { weatherAPIConfig } from '../../weatherAPIConfig';
const {useEffect, useState} = React;

function Row() {

    var [forecast, setForecast] = useState({});

    useEffect(()=>{
        fetchWeatherForecast("London").then((forecastObj)=>setForecast(forecastObj));
    }, [])

    return (
    <div>
        <div>API-key: {weatherAPIConfig.key}</div>
    <div>Result: {forecast.getWeatherDescription?.()}</div>
    </div>
  )
}

export default Row;

As a disclaimer, I haven't tested this code. But the gist of it is, have the "fetchweatherForecast" method return an object with methods that can access the "weatherForecastJSON" object. Then instantiate this object within your "Row.js" and render the data with the methods returned from the "weatherForecastJSON" object.

Edit: As noted by @Patrick Roberts, "forecast.getWeatherDescription()" would throw an error the first render. To remedy that, I've used optional chaining which would call the function only if it exists on the object. The alternative would be:

<div>Result: {forecast.getWeatherDescription ? forecast.getWeatherDescription() : ''}</div>