Select several checkboxes at once that seems to be images

Instead of manually selecting the check boxes of several pages,

I am using TamperMonkey to select all the check boxes with a small Javascript function.

The checkboxes get selected but the next step (SyncNow)for the procedure is greyed out.

I think it has to do with changing classes.

1. Is there another way to select the checkboxes with a 'click' via TamperMonkey?

or

2. How do I add an extra class that will hopefully not grey out the next step?

You can see the code that I have here:

https://codepen.io/Marina_2019/pen/dxXmZL

I tried this, and it did not work:

   function selectAll(){

            document.getElementById("AllInventorySelected").checked = true;

    }
}, false);

This function worked:

checkThem([].slice.call(document.querySelectorAll('input[type="checkbox"]')));


function checkThem(nodes) {
    nodes.forEach(function(n) { n.checked = true });
}

The problem is that the next after selecting all the check boxes are greyed out (unless I do it manually).

I noticed that a class gets added if I select the check boxes manually.

Code snippets are here:

https://codepen.io/Marina_2019/pen/dxXmZL