Electron. content-security-policy is fighting with render.js - html

Question

I have an electron js application:
const path = require('path');
const url = require('url');
const {app, BrowserWindow, ipcMain, nativeTheme, globalShortcut} = require('electron');
let win;
function createWindow() {
win = new BrowserWindow({
width: 1024,
height: 1024,
icon: path.join(__dirname, "web/img/app.png"),
fullscreen: true,
autoHideMenuBar: true,
webPreferences: {
preload: path.join(__dirname, "web/js/preload.js"),
}
});
win.loadURL(url.format({
pathname: path.join(__dirname, "web/html/index.html"),
protocol: 'file',
slashes: true
}));
win.webContents.openDevTools();
win.on('closed', () => {
win = null;
});
ipcMain.on('sys-shutdown', () => {
app.quit();
});
}
app.on('ready', createWindow);
app.on('window-all-closed', () => {
if (process.platform !== 'darwin') {
app.quit()
}
})
render.js:
window.onload=function() {
console.log("LOAD!");
const sys_shutdown = document.getElementById("SysShutdown");
sys_shutdown.addEventListener('click', async () => {
console.log('hello');
await window.sys.shutdown();
});
}
preload.js:
const { contextBridge, ipcRenderer } = require('electron');
contextBridge.exposeInMainWorld('sys', {
shutdown: () => ipcRenderer.send('sys-shutdown')
});
When I start a project, I get an error in the console:
Electron Security Warning (Insecure Content-Security-Policy) This renderer process has either no Content Security
Policy set or a policy with "unsafe-eval" enabled. This exposes users of
this app to unnecessary security risks.
For more information and help, consult
https://electronjs.org/docs/tutorial/security.
This warning will not show up
once the app is packaged.
I tried googling, but the solutions didn't work for me. I tried to allow all rights, but it didn't help either, I don't know what to do anymore...
P.S The console.log("LOAD") line works fine, but the code doesn't work any further.
Please help