You should use Percona XtraBackup 2.4 to backup data from 5.7
and you should use Percona XtraBackup 8 to backup data from 8.0,
but if you want to migrate from 5.7, you can use Percona XtraBackup 2.4 to backup and then start Percona XtraDB Cluster 8.0 on the data from backup, Percona XtraDB Cluster 8.0 will perform data upgrade automatically.
so Percona XtraBackup 8 can read the backup by Percona XtraBackup 2.4, also have the backup prepared for restore and then we copy the whole restore folder over the pxc 8.0.19 data directory, then when pxc 8.0.19 start using this new data directory content, it will just upgrade everything accordingly ?
so this can be installed on redhat linux 6.xx box with PXC 5.7.23?
but by this, it seems a lot easier than mysqldump ? by mysqldump can let me backup table schema + key + idnex only , data only and mysql logic only, right?
but it seems mysqldump can do multi threading too ?