In my case, for Linux ISOs, is only needed to login in my usual private trackers and re-download my leeched torrents. For more niche content, like old school TV shows in local language, I would rely in the community. For even more niche content, like tankoubons only available at the time on DD services, I have a specific job but also relying in the same back up provider that I'm using for personal data.

Also, as it's important to remind to everyone, you must encrypt your backup no matter where you store it.

I don't know of a pre-wrapped utility to do that, but assuming that this is a Linux system, here's a simple bash script that'd do it.

#!/bin/bash

# Set this.  Path to a new, not-yet-existing directory that will retain a copy of a list
# of your files.  You probably don't actually want this in /tmp, or
# it'll be wiped on reboot.

file_list_location=/tmp/storage-history

# Set this.  Path to location with files that you want to monitor.

path_to_monitor=path-to-monitor

# If the file list location doesn't yet exist, create it.
if [[ ! -d "$file_list_location" ]]; then
    mkdir "$file_list_location"
    git -C "$file_list_location" init
fi

# in case someone's checked out things at a different time
git -C "$file_list_location" checkout master
find "$path_to_monitor"|sort>"$file_list_location/files.txt"
git -C "$file_list_location" add "$file_list_location/files.txt"
git -C "$file_list_location" commit -m "Updated file list for $(date)"

That'll drop a text file at /tmp/storage-history/files.txt with a list of the files at that location, and create a git repo at /tmp/storage-history that will contain a history of that file.

When your drive array kerplodes or something, your files.txt file will probably become empty if the mount goes away, but you'll have a git repository containing a full history of your list of files, so you can go back to a list of the files there as they existed at any historical date.

Run that script nightly out of your crontab or something ($ crontab -e to edit your crontab).

As the script says, you need to choose a file_list_location (not /tmp, since that'll be wiped on reboot), and set path_to_monitor to wherever the tree of files is that you want to keep track of (like, /mnt/file_array or whatever).

You could save a bit of space by adding a line at the end to remove the current files.txt after generating the current git commit if you want. The next run will just regenerate files.txt anyway, and you can just use git to regenerate a copy of the file at for any historical day you want. If you're not familiar with git, $ git log to find the hashref for a given day, $ git checkout <hashref> to move where things were on that day.

EDIT: Moved the git checkout up.

My *arrstack DBs are part of my backed up portion, so they'll remember what I have downloaded in my non-backed up portion.

If you can't remember what you lost, did you really need it to begin with?

Unless it's personal memories of course.

Set up a job to write the file names of everything in your file system to a text file and make sure that text file gets backed up. I did that on my Unraid server for years in lieu of fully backing up the whole array.

servarr* and jellyfin are managing my movies and tv-shows

That should be part of the backup configuration. You select in the backup tool of choice what you backup. When you poose your array then you download that stuff again?