Just open up the browser’s console and run the following.
document.querySelectorAll("*").forEach(el => { if(el.offsetWidth > document.documentElement.offsetWidth) { console.log(el);}})
If an element on the page is wider than the document, it’ll get logged into the console.
Bonus:
Most browsers allow you to right click
on the elements that were printed to the console and scroll them into view. Unfortunately, you still have to fix the issue, but at least you’re one step closer to the solution.