How did you install freshrss, and what operating system are you using. If using docker, which docker image? There are multiple freshrss images. Do you explicitly map a docker volume or are you letting docker create an anonymous volume behind you back?
On my docker install using https://github.com/linuxserver/docker-freshrss the sqlite file is at this location inside the container at /var/www/FreshRSS/data/users/_/db.sqlite I have a bind mount mapping /var/www/FreshRSS/data to ./data . So, the sqlite file is in data/users/_/db.sqlite relative to the directory holding the docker-compose.yaml file.
Two suggestions
That will create a virtual session. If your ssh connection breaks, that virtual session still exists.
https://linuxize.com/post/how-to-use-linux-screen/
Use some sort of copy command that can deal with restarting a partial copy
rsync -av /mnt/4tb/* /mnt/14tb/