CoolClock
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Popup design broke possibly due to with chrome updates

Supplement:
I checked the console and found "document.registerElement is not a function". My guess is that this method is no longer supported due to chrome updates. I found the problem, but I don't know how to fix it...
Your assessment is correct - the popup uses the Custom Elements v0 API but Chrome recently dropped support for it in Chrome 80. To fix this, the page will have to be migrated to use Custom Elements v1 instead which has a different interface. In this case for example, document.registerElement is now customElements.define. I’m not sure how much effort it will take to do the migration.