Keep in mind that 5.7 will also be EOL in October 2023 and 8.0 will be your only option.
As Matthew points out, the application facing differences between 5.6 and 5.7 are very small. 8.0 is a different story with application compatibility and you should be considering your migration path to 8.0.
As far as 5.6 is concerned, it is EOL and we will not provide any more public builds of Percona Server 5.6. Supported platforms for 5.6 are also diminishing over time and one can not expect to be able to run 5.6 on new versions of the various distributions. As of today, the only supported non EOL distributions that you can run MySQL 5.6 on are CentOS 7 and 8, Debian 10, and Ubuntu 16.04 and 18.04 and many of these are going to become EOL within the next 12 months. EOL software and distributions present a serious security risk.
While we are going to make a best effort to keep the XtraBackup 2.4 series compatible with the last release of 5.6, we can not guarantee that future releases of the XtraBackup 2.4 series will be 100% compatible with 5.6. You can always stick with already released and compatible versions until you can get migrated.
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George O. Lorch III
Director of Server Engineering, Percona Server for MySQL, Percona XtraDB Cluster, and Percona XtraBackup