privacy – Delete Facebook Messenger messages for all users?

I'm trying to regain my privacy by removing some social networking apps. I start with Facebook and Messenger, because these are the ones I use the least, but I find that disabling or deleting your Facebook account does not delete your Messenger messages for other users: l. registration is retained. I would like to remove my presence completely, then, I have read these answers here and here. I have some questions:

  • Do these methods still work? These answers were given in 2015, 2016 and 2018, are they still applicable now?
  • Do I have to disable and reactivate my account, or can I just mark all my conversations as spam and then permanently delete my account? Is reactivation required for this method to work?
  • Finally, do I mark the entire thread of conversation as spam or just as my messages? Anyway, how is it?

Thank you in advance for helping me regain control of my privacy.