Can't create/write to file '/var/log/mariadb/mariadb.log'
Is SELinux running in enforcing mode? Run sestatus to find out. If so, it should be logging to the /var/log/audit/ directory. You can do grep mysql /var/log/audit/* to see if there are any problems related to "mysql" i.e. MariaDB.

Also, the correct privileges and SELinux context for the log directory and files are:

# ls -ldZ /var/log/mariadb/ drwxr-x---. mysql mysql 
system_u:object_r:mysqld_log_t:s0 /var/log/mariadb/
# ls -ldZ /var/log/mariadb/mariadb.log
-rw-r-----. mysql mysql system_u:object_r:mysqld_log_t:s0 /var/log/mariadb/mariadb.log


For instructions on how to set the right SELinux context, refer to the documentation: What to Do if MariaDB Doesn't Start - SELinux and MariaDB Path Changes.