You can configure Syncthing to keep deleted/changed files for some time. So you could connect a Raspberry Pi to store everything read-only.

But there is still a difference between the owner being able to take my public content offline and them knowing my private location. However, since my instance is non commercial and doesn't make any money by tracking it shouldn't be that bad to trust them on that.

Thanks for your effort :) So it seems like you have to trust your instance?