MariaDB 10.5.11 cannot do SST when binary log is enabled on donor

If we do a SST on Debian 10 from a donor with binary logging DISABLED SST works without problems.
If we do a SST on Debian 10 from the same donor with binary logging ENABLED SST fails with error (on donor)
:
tail: cannot open 'mysql-bin.index' for reading: No such file or directory
[ERROR] WSREP: Failed to read from: wsrep_sst_rsync --role 'donor' --address '188.34.159.129:4444/rsync_sst' --local-port '3306' --socket '/run/mysqld/mysqld.sock' --datadir '/var/lib/mysql/' --gtid 'eb3f6b4b-ea20-11eb-83bb-86bdcfe45310:25' --gtid-domain-id '0' --binlog 'binary-log' --mysqld-args --wsrep-new-cluster --wsrep_start_position=eb3f6b4b-ea20-11eb-83bb-86bdcfe45310:1
[ERROR] WSREP: Process completed with error: wsrep_sst_rsync --role 'donor' --address '188.34.159.129:4444/rsync_sst' --local-port '3306' --socket '/run/mysqld/mysqld.sock' --datadir '/var/lib/mysql/' --gtid 'eb3f6b4b-ea20-11eb-83bb-86bdcfe45310:25' --gtid-domain-id '0' --binlog 'binary-log' --mysqld-args --wsrep-new-cluster --wsrep_start_position=eb3f6b4b-ea20-11eb-83bb-86bdcfe45310:1: 1 (Operation not permitted)

We tried to disable apparmor but it did not change anything...