Below there is again a very special article. I think the people who are affected will understand what it is about. All others must be said that the next article will be for a wider audience again.
Originally, I had realized the transparent corners using own paths, which I created and filled as shown below.
ctx.globalCompositeOperation = "copy";
ctx.fillStyle = "rgba(0,0,0,0.0)";
After some googling I found out that the globalCompositeOperation “copy” is not correctly implemented/supported anymore. […]