I don’t have a solution really, but I’m also thinking along your lines.

For files I share with my girlfriend, I have set up syncthing. So my server and our phones have a copy of the files, I like this solution. But it wouldn’t work for large amounts of data.

For my server stuff, it is backed up encrypted on backblaze. so I guess that is lost. Most files are also rsynced onto a usb drive connected to a raspberry pi (not encrypted). So that should be accessible, except for a linux’y filesystem (probably ext4) that doesn’t work on windows