How to detect if I am in 'console' mode

By default for console:

Yii::$app->id == 'basic-console'

And for web application:

Yii::$app->id == 'basic'

Yii::$app->id stores the id of the loaded configuration params. By default for console application it is 'basic-console' and for web application it is 'basic' (defined in configuration file)

Correct variant

Yii::$app->request->isConsoleRequest

You can use

if (Yii::$app instanceof \yii\console\Application)

for console, and

if (Yii::$app instanceof \yii\web\Application)

for web.

There is a simpler way to figure this out without going through the Yii objects

if (php_sapi_name() == "cli") {
    return;
}

...and it works for all PHP scripts ...and it is lighter