Well this came up in the post where people said their Reddit posts were being restored. Even when the user deleted their account mind you. Basically there is something in the reddit TOS that with everything you post you give up your rights to that and it becomes reddit's content. But that was from a US legal perspective. I'm not sure how that would hold up against GDPR laws.
Edit, this is the post I'm referring to: https://lemmy.world/post/186613
