To work around the issue, navigate to

C:\Program Files\Unity\Hub\Editor\2019.3.0b7\Editor\Data\PlaybackEngines\WebGLSupport\BuildTools\

and edit UnityLoader.js and find "instantiate:" function with lines

var Module = gameInstance.Module;
Module.canvas = document.createElement("canvas");

after those two lines, put in

// Disable Microsoft Edge (Chromium-based, tested on 44.17763.771.0) from dragging the whole canvas as an image object when one drags with a mouse over the canvas
Module.canvas.ondragstart = function(e) { e.preventDefault(); };

That will remove Edge from attempting to start an image drag on the canvas.

Another workaround, slightly hacky, but self-contained to user template, is to edit the main html file, find

<script>
var gameInstance = UnityLoader.instantiate("gameContainer", "Build/game.json", {onProgress: UnityProgress});
</script>

and change it to

<script>
var gameInstance = UnityLoader.instantiate("gameContainer", "Build/game.json", {onProgress: UnityProgress});
function disableEdgeCanvasDrag() {
var canvas = document.querySelector('canvas');
if (!canvas) return setTimeout(disableEdgeCanvasDrag, 1000);
canvas.ondragstart = function(e) { e.preventDefault(); };
}
disableEdgeCanvasDrag();
</script>