Insert "pid-file=/run/mariadb/mariadb.pid" into installed "/etc/my.cnf.d/server.cnf" and the directory does not get created.
"/usr/lib/tmpfiles.d/mariadb.conf" contains only one line:
d /var/lib/mysql 0755 mysql mysql -
Have to manually create and modify new "/etc/tmpfiles.d/mariadb.conf" to include the requisite "d /run/mariadb 0755 mysql mysql -".
There are no instructions/notes/warnings about this - just the error message:
[ERROR] mysqld: Can't create/write to file '/run/mariadb/mariadb.pid'
(Errcode: 2 "No such file or directory")
This was not a problem with MariaDB-10.3.28.