Solved!
Had to change the file in /etc/systemd/system/ghost_danielesalatti-com.service and swap the node version from:
/home/ubuntu/.nvm/versions/node/v12.8.3/bin/node /home/ubuntu/.nvm/versions/node/v12.8.3/bin/ghost run
to:
/home/ubuntu/.nvm/versions/node/v14.15.4/bin/node /home/ubuntu/.nvm/versions/node/v14.15.4/bin/ghost run
And then run:
systemctl daemon-reload
After that ghost restart and everything works again.