Read the instructions on the project screen. If you can't see it, read how to do it in this box: How to enable WebGL: 1. Click on a new tab, and enter this address: Google Chrome: chrome://flags Microsoft Edge: edge://flags Other browsers: (browser name)://flags 2. Find the WebGL section and enable it. It may require you to restart your browser. 3. Go back to Scratch, go to any project, and everything should go back to normal.
Since July 23rd, 2020, The Scratch Team made some changes to the project runner technology or something. It now requires WebGL to run Scratch Projects. I figured out how to fix it. And it's all in here. I checked on mobile, and it also has WebGL on its own. So, that is good.
