I have been curious of this one since it's a feature that mastodon has, and while I understand with FOSS software anyone can disable that, but usually people don't and if I knew they were doing that I would defederate them.
Comment and post edits and deletes are federated. OP probably means account deletion. Currently, if you delete your Lemmy account, it does not federate, so your old comments and posts stick around on other instances, I believe even with your old username attached.
They are federated, but it's not reliable. Lot of room for improvement. I have comments where the deletion never federated so they're basically on other servers forever.
I've made edits and deletes, and as far as I can tell, once the instances sync up, those edits/deletes are synced as well - I have noticed a delay, but it usually kicks in like overnight (for example) when I make a change using my account on lemm.ee for my account on lemmy.world to see it, etc.
I cannot see how distributed systems like Fediverse can be GDPR compliment unless you lock out the system admins of the instance they host. Good DevOps requires frequent backups; it also requires offline backups.
It is one of the only good things about a centralised system - the entity that holds the data can be held accountable for not being compliant and other such things. Many mere mortals can collectively group together to fight against the goliath.
It requires too many resources to chase after the small instance owners of a distributed system like Fediverse. Just like how 3 letter agencies chase after the people who like to ride the seas in their wooden boats. The 3 letter agencies have spent a lot of resources attempting to shut it down but they've never come close.
I have just gotten in the habit of editing first and adding the same two characters. Then I delete. If I want to in the future, I can potentially search based on those characters. I mostly just delete because I don't want to see the replies any more, or get reminded about something every time I view my profile.