Make doIt function public

[Anubarak]

I found a strange issue or at least a very edge case scenario in your plugin.
When there is an internal call in Craft for

Craft::$app->getFields()->getAllFields();

and there are no fields yet, it will fetch all of them from the DB and loop those results to populate fields.
So it will call

public function createField($config): FieldInterface

and it does

$field = ComponentHelper::createComponent($config, FieldInterface::class);

That function tries to validate it

static::validateComponentClass($class, $instanceOf, true);

Remeber $this->fields is still [] because no field is created yet ¯_(ツ)_/¯
Unfortunately if it comes really from a plugin, Craft will do the following

// If it comes from a plugin, make sure the plugin is installed
$pluginsService = Craft::$app->getPlugins();
$pluginHandle = $pluginsService->getPluginHandleByClass($class);
if ($pluginHandle !== null && !$pluginsService->isPluginEnabled($pluginHandle)) {

    /**
     * Returns whether a given plugin is installed and enabled.
     *
     * @param string $handle The plugin handle
     * @return bool
     */
    public function isPluginEnabled(string $handle): bool
    {
        $this->loadPlugins();
        return isset($this->_enabledPluginInfo[$handle]);
    }

The function $this->loadPlugins(); is the key point here.... because it does what the name let's you think.. it loads all plugins and trigger the event

if ($this->hasEventHandlers(self::EVENT_AFTER_LOAD_PLUGINS)) {
    $this->trigger(self::EVENT_AFTER_LOAD_PLUGINS);
}

Remeber when I told $this->fields is still an empty array? That's even now the case when your event is triggert

// Handler: EVENT_AFTER_LOAD_PLUGINS
Event::on(
    Plugins::class,
    Plugins::EVENT_AFTER_LOAD_PLUGINS,
    function () {
        $this->doIt();
    }
);

So $fields = Craft::$app->getFields()->getAllFields(); returns an empty array and no field will be marked with a wheel.
Currently my work-around is to copy your code in my custom module and run it again, but it would be easier to call the function doIt twice

[mmikkel]

I don't believe this is relevant anymore since I moved the Craft::$app->getUser()->getIsAdmin() query into a EVENT_AFTER_LOAD_PLUGINS handler w/ CP Field Inspect 1.0.7. Closing.