Hi,
twindb-backup bundles xtrabackup-2.4, which covers MySQL/Percona 5.6 + 5.7.
As a workaround for now it is possible to specify an xtrabackup binary for 8.0 (--xtrabackup-binary=/usr/bin/xtrabackup).
Or you can put that in a config file /etc/twindb/twindb-backup.cfg:
[mysql]
...
xtrabackup_binary=/path/to/xtrabackup
Best,
Aleks