Kint Display

The only reason that I can see right now as for why Kint would not work and default to the Symfony var dumper would be that the Kint library is not installed on your Drupal installation.

You can see whether it is installed via composer show kint-php/kint and install (if necessary) via composer require-dev kint-php/kint.

If that is not the problem, feel free to reach out again.

It is also good to note that the Kint dumper is only a nicer and more structured way to view information about an object in most cases (meaning that it is not a necessity). The var dumper (that you are seeing right now) should also provide all information about the object, just differently.
Kint is also unable to show object methods anyway contrary to what you requested.

I think this is solved. Might also have been an issue on the reporters side.