I can't figure out why my program won't turn swap in Tic Tac Toe

Question

When I set o_Turn to true, I can place a circle, then another one, and so on, and it doesn't swap to a cross, and when I set o_Turn to false, I can place a cross, then another one, and so on, and it doesn't swap to a circle, I'm a total beginner when it comes to JS and I thought making this would be an easy introduction to it, anyone got any idea why it won't turn swap?

tictactoe.js

const X_CLASS = "x"
const O_CLASS = "circle"
const COMBINATIONS = [
    [0,1,2],[0,3,6],[0,4,8],
    [1,4,7],[2,4,6],[2,5,8],
    [0,4,8],[3,4,5],[6,7,8]
    ]

const cellElements = document.querySelectorAll('[data-cell]')
const boardElement = document.getElementById('board')
const winningMessageElement = document.getElementById('winningMessage')
const restartButton = document.getElementById('restartButton')
const winningMessageTextElement = document.getElementById('winningMessageText')
let o_Turn = false

startGame()

restartButton.addEventListener('click', startGame)

function startGame(){
    o_Turn = true
    cellElements.forEach(cell => {
        cell.classList.remove(X_CLASS)
        cell.classList.remove(O_CLASS)
        cell.removeEventListener('click', handleCellClick)
        cell.addEventListener('click', handleCellClick, {once: true})
    })
    setBoardHoverClass()
    winningMessageElement.classList.remove('show')
}

function handleCellClick(e){
    const cell = e.target
    const currentClass = o_Turn ? O_CLASS : X_CLASS
    placeMark(cell, currentClass)
    if (checkWin(currentClass)){
        endGame(false) // somebody won
    }else if (isDraw()) {
        endGame(true) // game is draw
    }else {
        swapTurns()
        setBoardHoverClass()
    }
}

function endGame(draw){
    if (draw) {
        winningMessageTextElement.innerText = "DRAW"
    } else {
        winningMessageTextElement.innerText = `${o_Turn ? "O" : "X"} wins!`
    }
    winningMessageElement.classList.add('show')
}

function isDraw() {
    return [...cellElements].every(cell => {
        return cell.classList.contains(X_CLASS) || cell.classList.contains(O_CLASS)
    })
}
function placeMark(cell, currentClass) {
    cell.classList.add(currentClass)
}

function swapTurns() {
    o_Turn = !o_Turn
}
function setBoardHoverClass() {
    boardElement.classList.remove(X_CLASS)
    boardElement.classList.remove(O_CLASS)
    if (o_Turn) {
        boardElement.classList.add(O_CLASS)
    } else {
        boardElement.classList.add(X_CLASS)
    }
}
function checkWin(currentClass) {
    return WINNING_COMBINATIONS.some(combination => {
        return combination.every(index => {
            return cellElements[index].classList.contains(currentClass)
        })
    })
}