Once backup reaches the "Waiting for copy thread to read lsn" step (it can take several minutes to complete this step) connections can't reach the server, resulting in application downtime until backups ends.

Command:

mariabackup --backup --user=root --no-version-check --socket=/run/mysqld/mysqld.sock --open-files-limit=65536 --throttle=50000 --parallel=1 --ftwrl-wait-timeout=300 --ftwrl-wait-threshold=86400 --ftwrl-wait-query-type=update --target-dir=/dev/shm/backup

When the script runs, it CTRL+C is hit, connections are immediately accepted again on MariaDB 10.8.5 server. By connections I mean READ and/or WRITE, as from application point of view, it looks like MariaDB server hangs.

Happy to help debug this (nothing is logged on MariaDB server logs).