Your comments

I use this workaround with the library https://html2canvas.hertzen.com/ 

Open a javascript console and paste this code. This will open a new tab with the image you can save.

fetch('https://html2canvas.hertzen.com/dist/html2canvas.min.js')
   .then(response => response.text())
   .then(text => eval(text))
   .then(() => {
           var pspace = document.getElementsByClassName('printSpace')[0]
           var w = pspace.width.baseVal.value;
           var h = pspace.height.baseVal.value;
           html2canvas(document.getElementsByTagName('board-diagramcontainer')[0], {width: w, height: h}).then(canvas => {
           var newTab = window.open();
        newTab.document.body.innerHTML = '<img src="'+ canvas.toDataURL() +'">';
    });
});

Of course, use this code under your responsibility. I only tested with chrome.