[Dúvida] Jogo da Memória falho

No caso dos javascript, dividi em dois codigos :

let game = {
    lockMode: false,
    firstCard: null,
    secondCard: null,

    setCard: function (id) {
        let card = this.cards.filter(card => card.id === id)[0];
        console.log(card);
        if (card.flipped || this.lockMode) {
            return false;
        }

        if (!this.firstCard) {
            this.firstCard = card;
            this.firstCard.flipped = true;
            return true;
        } else {
            this.secondCard = card;
            this.secondCard.flipped = true;
            this.lockMode = true;
            return true;
        }
    },

    checkMatch: function () {
        if (!this.firstCard || !this.secondCard) {
            return false;
        }
        return this.firstCard.icon === this.secondCard.icon;
    },

    clearCards: function () {
        this.firstCard = null;
        this.secondCard = null;
        this.lockMode = false;
    },

    unflipCards: function () {
        this.firstCard.flipped = false;
        this.secondCard.flipped = false;
        this.clearCards();
    },

    checkGameOver: function () {
        return this.cards.filter(card => !card.flipped).length == 0;
    },

    techs: ['bootstrap', 'css', 'electron', 'firebase', 'html', 'javascript', 'jquery', 'mongo', 'node', 'react'],

    cards: null,

    createCardsFromTechs: function () {
        this.cards = [];
        this.techs.forEach((tech) => {
            this.cards.push(this.createPairFromTech(tech));
        });
        this.cards = this.cards.flatMap(pair => pair);
        this.shuffleCards();
        return this.cards;
    },

    createPairFromTech: function (tech) {
        return [{
            id: this.createIdWithTech(tech),
            icon: tech,
            flipped: false,
        }, {
            id: this.createIdWithTech(tech),
            icon: tech,
            flipped: false,
        }];
    },

    createIdWithTech: function (tech) {
        return tech + parseInt(Math.random() * 1000);
    },

    shuffleCards: function () {
        let currentIndex = this.cards.length;
        let randomIndex = 0;
        while (currentIndex !== 0) {
            randomIndex = Math.floor(Math.random() * currentIndex);
            currentIndex--;
            [this.cards[randomIndex], this.cards[currentIndex]] = [this.cards[currentIndex], this.cards[randomIndex]];
        }
    }
};

E por ultimo, o script.js:

const FRONT = "card_front";
const BACK = "card_back";
const CARD = "card";
const ICON = "icon";

startGame();

function startGame() {
    initializeCards(game.createCardsFromTechs());
}

function initializeCards(cards) {
    let gameBoard = document.getElementById("gameBoard");
    gameBoard.innerHTML = '';
    cards.forEach(card => {
        let cardElement = document.createElement('div');
        cardElement.id = card.id;
        cardElement.classList.add(CARD);
        cardElement.dataset.icon = card.icon;

        createCardContent(card, cardElement);

        cardElement.addEventListener('click', flipCard);
        gameBoard.appendChild(cardElement);
    });
}

function createCardContent(card, cardElement) {
    createCardFace(FRONT, card, cardElement);
    createCardFace(BACK, card, cardElement);
}

function createCardFace(face, card, element) {
    let cardElementFace = document.createElement('div');
    cardElementFace.classList.add(face);
    if (face === FRONT) {
        let iconElement = document.createElement('img');
        iconElement.classList.add(ICON);
        iconElement.src = "./assets/images/" + card.icon + ".png";
        cardElementFace.appendChild(iconElement);
    } else {
        cardElementFace.innerHTML = "</>";
    }
    element.appendChild(cardElementFace);
}

function flipCard() {
    if (game.setCard(this.id)) {
        this.classList.add("flip");
        if (game.secondCard) {
            if (game.checkMatch()) {
                game.clearCards();
                if (game.checkGameOver()) {
                    let gameOverLayer = document.getElementById("gameOver");
                    gameOverLayer.style.display = 'flex';
                }
            } else {
                setTimeout(() => {
                    let firstCardView = document.getElementById(game.firstCard.id);
                    let secondCardView = document.getElementById(game.secondCard.id);

                    firstCardView.classList.remove('flip');
                    secondCardView.classList.remove('flip');
                    game.unflipCards();
                }, 1000);
            }
        }
    }
}

function restart() {
    game.clearCards();
    startGame();
    let gameOverLayer = document.getElementById("gameOver");
    gameOverLayer.style.display = 'none';
}

Oii Guilherme, tudo bem?

No console do navegador, há erros de carregamento de scripts?

Pra te ajudar, peço que você coloque o seu projeto em um repositório do GitHub, assim posso testar melhor e entender como você organizou as pastas e verificar se não é erro de importação.

Um abraço.