Can posts and comments on Lemmy be fully deleted since they still appear with the option to "undelete" after doing so?
I noticed when you delete a post or comment on Lemmy it still shows up on my account with the option to "undelete" it which fully restores it and makes it public again.
Does this mean you can't fully delete them and basically only "hide" them from the community but they will still stay on the server forever? Or is there any option to fully delete them or will that happen after some time?
No. And simply put, this is because of the nature of the fediverse. You post something then it's on anyone listening's server. Lemmy or otherwise. Now, when you delete you send a delete request to all of those servers too.
Here's the thing. What if someone forks Lemmy or just has their own server type. They don't HAVE to implement delete. It could still be there. Maybe it's hidden, but it's there.
Now assume any government or corp is listening to the fediverse.
So no. We're open, no one can take us down, but, know that anyone can listen, and they can do whatever they want
By using the fediverse you blast that comment out to any server hosted anywhere in the world hosted by anyone. Even if an instance is hosted in one of those countries it would have to be following and enforced, and you would have to follow up with every server you sent it to and verify (somehow, remember they don't need to actually have a public frontend) that your comment was deleted.
So, no. I would not ever assume that on the fediverse. Free and open means completely free and completely open. It's like the 90s here, there's no such thing as delete.