First make sure that your sytem has correct value for "LimitNOFILE"
Open this file: /etc/systemd/system/mariadb.service.d/migrated-from-my.cnf-settings.conf
Check for this variable
# converted using /usr/bin/mariadb-service-convert
#
[Service]
LimitNOFILE=512 --> "65536"
Save this file.
Now any changes inside my.cnf are applicable.
System might ask for
# systemctl daemon-reload
Now restart mariadb service
# systemctl restart mariadb
# systemctl status mariadb -l
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