My solution is:

go through every chat that you had in the last 2 years, and "mute" it.

That way you won't get the red dot notifying you about it when you log into Facebook, and you can blissfully ignore any message there. You might still want to check messages there every once in a while (every couple of weeks, maybe)

If you have other contacts (advertised on your Facebook about page, even!) and you let your friends know to avoid contacting you on Facebook, I think they shouldn't expect you to be alert and quick to reply to their messages on such a platform

Your parent's explicit usecase is "sometimes people make ad-hoc plans with me through messenger", and ignoring those for weeks on end sort of defeats the purpose and encourages those folks to not make plans with them...

That is the issue. I'd be more willing to try training my friends to contact me through other means except that, having recently moved to a new city where I knew no one, none of the people I currently spend time with IRL actually have much invested yet in being my friend, so tossing up hurdles seems unwise.

here's an easier protip: use uBlock Origin, and completely hide the right-hand column.

Presumably you mean uMatrix?

No. I'm talking about uBlock Origin, which has a tool (see the button with the little eyedrop icon) which you can use to click on elements of the screen to hide them and save that as a rule. I think this is a bit simpler than uMatrix's UI.

Oh sorry, I completely misunderstood.

I didn't realise you meant visual column - I thought you meant 'use X and in it disable everything in the right-hand column'; since uBlock Origin doesn't have a columnar UI, I assumed you meant uMatrix. :)