I have log_bin specified to the data directory:
In the mariabackup output, I see that mariabackup copies the binary logs to the backup directory:
 2022-06-06 19:22:58 Compressing /var/lib/mysql/mariadb.000270 to /backupdisk/diff-2022-06-06_19-07-01/mariadb.000270.qp
This is needless consumption of space on the backup disk.
I did not find a command-line switch to disable copying the binary logs, I think this is a bug in mariabackup to just copy all the files that are in the data directory.
Specifying a custom binlog directory is NOT a work-around for this issue. It does not seam that the general log is stored with the backup, so why can the binary logs not be excepted?
Earlier bakup runs (with a different mariabackup version) did not show this issue, it seams some thing changed in mariabackup.
My current version:
mariabackup based on MariaDB server 10.3.35-MariaDB Linux (x86_64)
 2022-06-06 10:26:07 Using server version 10.3.31-MariaDB-log
/usr/bin/mariabackup based on MariaDB server 10.3.35-MariaDB Linux (x86_64)
The older runs were slightly different versions:
 2022-03-23 00:07:01 Using server version 10.3.31-MariaDB-log
/usr/bin/mariabackup based on MariaDB server 10.3.34-MariaDB Linux (x86_64)