As per BackupPC documentation Perl 5.28 or newer is required. https://backuppc.github.io/backuppc/BackupPC.html#Requirements Packages depent on 5.26 (including p5-BackupPC-XS)
Why do you think that Perl 5.28 or newer is required? The BackupPC documentation clearly states "Perl version 5.8.0 or later." What is the problem you are trying to solve?
I'm sorry I misread the documentation.