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When you cannot share at a meeting, it is a good advance to check if you actually allowed your Google Chrome browser to access your devices (micro/cam). If not, you will be stuck in "processing" mode forever and cannot request to share.
In the address bar of Google Chrome you can see a camera icon on the far right; please click on it and a menu will appear. It will tell you if you set this site to always allow your camera/microphone or to deny - it also lists which devices are being used so this is a good place to search when you have problems with your audio/video. Please check attached screenshot for details.