inodes quantity depends on cluster size and partition size, so if you want more inodes on same disk space - you must decrease cluster size,
if you can't change cluster size - just increase disk space (extend partition).
in your case you must find out what uses so many inodes. (mail, session files, CMS cache files etc.)
it depends on your filesystem, resizing for LVM's or soft/hard raid or for regular partition can be done through different ways.
or you are talking about how to find out what uses so many inodes?
in such case check quota from directadmin, start from largest accounts.
Inside / usr there was a directory where the warning tickets created by the server were stored. They had been stored there since 2018, apparently the server was installed. Each one occupied an inode and they were saturating everything.