After a recent system update, remote debugging stopped working. It's possible (even likely) that Chrome auto-updated itself around the same time. Remote Debugging via Qt no longer works, with this error in the JavaScript console of Chrome:

Uncaught TypeError: document.registerElement is not a function
{{ at Object.UI.registerCustomElement (shell.js:formatted:18064)}}
{{ at shell.js:formatted:18178}}
{{ at shell.js:formatted:18266}}
devtools_app.js:formatted:2606 Uncaught ReferenceError: SDK is not defined
{{ at devtools_app.js:formatted:2606}}

The code in question (from shell.js) is this:

UI.registerCustomElement = function(localName, typeExtension, prototype) {
{{ return document.registerElement(typeExtension, {}}
{{ prototype: Object.create(prototype),}}
{{ extends: localName}}
{{ });}}
}

I asked about it on Stack Overflow:
https://stackoverflow.com/questions/60292131/angular-8-chrome-developer-tools-no-longer-work/60315607#60315607

and if I'm understanding the answer correctly, QWebEngine needs an upgrade in order to be able to continue doing remote debugging on Chrome, now that WebComponents V0 is no longer available.

Version of Chrome that is incompatible (and presumably later versions):
80.0.3987.116 (Official Build) (64-bit)

Testing with an older build of Chromium (77.0.3823.0), it still works there.