Drupal 8: Node form submit/update - how to redirect to a custom page with an code-based approach different than hook_form_alter() I have Drupal 8 installation, with a custom content type.
I would like to redirect to a specific page after node form submission.

What I have tried so far:
Using hook_form_alter() and it works, but that's not the point here.

What I want to achieve:
Delivering the same functionality in a new OOP code based way.

What I have found so far:
https://www.thirdandgrove.com/redirecting-node-pages-drupal-8

This example shows the replacement for the old hook_init().

Update 1:
Rules module can achieve the desired functionality.

Update 2:
Node_save_redirect module can achieve the desired functionality.

Update 3: A possible answer
https://www.foreach.be/blog/how-manipulate-forms-drupal-8
can someone with enough D8 experience actually confirm if that's actually the official way of doing things ?

Regards,
Oleg
While the other solution is perfectly valid, I mark this answer as accepted since it comes closer to what I was looking in first place - the new way to alter forms.

Eventually the solution can be found right here:
https://www.foreach.be/blog/how-manipulate-forms-drupal-8 

In summary (quoted from the article):
1 ) The first step is to write a service that intercepts the original UserLoginForm and directs to the adapted form

2)  Changed the route to return the adapted NewUserLoginForm instead of the original UserLoginForm

3) The new form extends the old form and inside the buildForm method you add in the beginning 

$form = parent::buildForm($form, $form_state);


This step was missing in the example tere