Lumen 6.3 and PHP 7.4

In the Lumen 5.7 repo, the composer.json shows the below for PHP:

        "php": "^7.1.3",

And per the Composer Version Constraints below, I would think PHP 7.4 should be compatible:

The ^ operator behaves very similarly but it sticks closer to semantic versioning, and will always allow non-breaking updates. For example ^1.2.3 is equivalent to >=1.2.3 <2.0.0 as none of the releases until 2.0 should break backwards compatibility. For pre-1.0 versions it also acts with safety in mind and treats ^0.3 as >=0.3.0 <0.4.0.

The Lumen 6.x GitHub repr shows the below in its composer.json file. So one would think that upgrading to this version would not be of much help in your scenario.

"php": "^7.2",

If you didn't already, I suggest running through all of the common update pitfalls, i.e. composer dump-autoload etc. and see if that's the issue at hand.

Its an old question, but the ServiceProvider is looking for config that has not yet been registered. Lumen does not automatically search the config directory, but instead each config file must be added into the /bootstrap/app.php file before the ServiceProvider class is called.

For example, $app->configure('view');

Which should come before $app->withEloquent();