Floocus is what you are looking for. It can store the file on any webdav, gdrive, git or Nextcloud storage. I use it to sync my bookmarks between Browsers and systems
The message says it all. DNS rebind means a domain name is pointing back to an internal IP address. You need to make an exception in pfsense for your domain dash.homelab.duckdns.org
Removed Kavita since they started Kavita+ and the floating donate button, which can only be removed if you pay. Never again
I use Komga instead