Honestly this doesn't fit my usecase. If I understand it correctly, it is just like any other retention policy meaning it is not related to the fact that the attachment was deleted by user, but it just deletes everything after a certain point.

I don't mind storing things that people can access for many years - if I wanna see that funny picture from 10 years ago, I should be able to find it (even though GUI in Element sucks for that now). But what I do care about are things they uploaded accidentally or that they wanted to delete for whatever reason and it stayed on my server.