By design; notes cannot vanish, there is no guarantee that every relay out there will ever delete your note.
At best they can only pinky promise to you that it’s gone, then still another relay could be holding any note for any undisclosed amount of time 😉
So true :) after posting my question I had same idea.
Thanks for your answer
This is technically true, but practically it is feasible.
I don't think there is a popular client that helps you do this, but you would need to find relays that you can trust that require you to authenticate and that don't just spread your posts to anyone.
If it is only delivered to "your friends" (based on a list or your follower list), this limits the risk already.
If it never gets broadcast to other relays, this limits the risk.
Then it only requires using a type of note that supports expiry dates.
Not technically guaranteed, but good enough for most people.
