I think it's safe to assume most anything you delete from a web app gets a deleted boolean or timestamp field set and the content persists in the database indefinitely.
In my experience I've found it rare that user content is ever actually permanently deleted for various reasons.
I assume that storage has gotten so cheap now that storing everything forever is feasible for companies? I always knew they had to retain content for X period of time, to comply with laws about data retention for criminal investigations, but I always assumed (from reading about it 10+ years ago) that because of how much extra storage space all the "deleted" content would take up, that it wouldn't be feasible for them to do it long-term for everything. I knew that would become a moot point eventually, and I suppose that is now.
It is. I recall seeing some documentary about Facebook for the exact same thing - that it was cheaper to buy new hard drives and inactivate old content than it is to try to permanently scrub old content, and that was probably 10 years ago.
Yeah that's how most of them work. On some platforms (e.g. Reddit) if you do a full data request you'll see all your deleted comments as it's still there in the database, just hidden from public view.
In my experience I've found it rare that user content is ever actually permanently deleted for various reasons.