

You cannot meaningfully delete your posts or comments. That’s not because of any issue with lemmy, but because you posted them publicly. They will be archived and indexed in other services.It is always best to remember that all your activity here is public, and will be linked to your username. Given that, you may wish to minimise any personally identifying information you post, and use several accounts to split up your activities by topic.
I don’t believe other instances will receive any sort of deletion request from lemm.ee, it’ll just go away. Any instances that have a copy of your posts or comments will keep them for as long as they wish. Even if you manually delete the comments and lemm.ee federates that action out, there is no guarantee that any other server will actually act on it, and you can be certain that archiving services will not.
Ultimately it comes down to the fact that you posted, commented or voted in public, and that will remain public indefinitely. That’s as much down to howpublic data is captured by other entities as it is to the concept of federation.
It’s a bit of a stretch calling it a plastic, as it’s not petroleum based from what I’ve read.