Anything you post on the internet is public knowledge forever. End of discussion. Most people won’t care at all, in most cases almost nobody or perhaps even literally nobody will ever even see it, but the harder you try to hide it, the more the Streisand Effect will magnify it until eventually everyone knows about it.

Anyone telling you they’ll delete your data from the internet without clarifying that it is in fact impossible, is at worst deliberately lying to you usually for their own benefit, and at best making a promise they literally have zero ability to keep.

I would hope that Fediverse services will never lie to you and tell you your data is deleted, because it can’t be.