Your ssd should be automatically mounted in /media directory.
/storage/8tb-ssd is not standard libreelec directory and it would exist on /storage only if some of your actions created it. That directory does not contain librelec system data. It can contain only your personal data files and maybe indexing information that librelec created when indexing those files.
If I were you, I would be moving all /storage/8tb-ssd data into dedicated directory on 8TB SSD. It is relatively easy to do, if system utils addon is installed. If you never needed to install that addon, you probably won't be able to add it with full /storage and only Unix CLI commands can be used to move stuff out.
64GB SD card won't be enough, if you continue filling up /storage/8tb-ssd while thinking that you are writing to 8TB device.