Custom extension won't appear in Accounts page

I am trying to develop a custom extension, in accordance to Adding a Custom Sidebar Widget.

I’ve basically copy-pasted the code inside the proper files and built a custom extension as in Setting Up a Front-End Extension Module. It’s easy to see that in the console it prints “sidebar widget register” and “loaded”. Yet the extension never loads, seemingly?

Did you run the command:
yarn run build-dev:<name-of-your-extension> --watch

Yes, I did. Not only that, I had to copy the files created in public/extensions to dist/extensions so it could work. It is also worth noting that I had to remove polyfills from angular.json else it wouldn’t compile (gave me can’t resolve polyfill.ts in extensions//app/src/polyfills).

What about run the command ./bin/console cache:clear

Still nothing. I ran composer install after building the module as well, which should have taken care of clearing the cache by the end of its execution.