And apparently there’s no CLI option to compress it. Just in case you may want to, you’re free to just don’t…
Yet, even if not advertised here, for those who would like to, a setting is available to force the old behavior and compress all your backups
sudo yunohost settings set backup.compress_tar_archives -v true
EDIT: Correction, this setting breaks the backup as soon as you delete a backup…
It deletes the tar.gz file but not the symbolic link which break all the backup process afterward… 