you have to use borg’s python virtual environment
Read here: [Borg & Borg Server] Deduplicated, encrypted and remote backups - #130 by Aristid
or
define environment variables (as read in the documentation):
app=borg
PATH="/var/www/$app/venv/bin/:$PATH"
export BORG_PASSPHRASE="$(sudo yunohost app setting $app passphrase)"
export BORG_RSH="ssh -i /root/.ssh/id_${app}_ed25519 -oStrictHostKeyChecking=yes"
repository="$(sudo yunohost app setting $app repository)"