Harder here than on centralized platforms because everything you posted here has been copied to other servers which might ignore your requests to delete things.

deleted by creator

No.

As redwizard said, you can edit all your posts and request a purge, but that doesn’t mean that the administrators of instances federated with yours will actually do so.

It’s also trivial to have a private fork whose purge process is “log that a purge was requested for the following db items”.

Federation means you can never vanish. Even if it did, people screenshot stuff now more than ever.

Edit all your posts then request a purge.

You should be able to contact your admins so they purge your account. Purged accounts have all the content they ever published scrubbed from all databases on Lemmy. I’m not entirely sure how it works if there’s an instance that is defederated from your home instance after you post something and it gets federated to them, I assume it wouldn’t be deleted in that case so it would still be available online there, but certainly a lot harder to track down.

deleted by creator

Even if you managed to delete the posts from all federated servers, they will still be archived in various places like the wayback machine and similar.

Better to only post what you’re comfortable sharing forever.