How did I fix «Unable to load dynamic library '/usr/lib64/php/modules/'» / «No such file or directory» for PHP 7.1 in CentOS 7.6?

Step 1

yum search mbstring


Step 2

yum install php71-php-mbstring.x86_64

Step 3

find / -name "" -print 2>/dev/null


Step 4

ln -s /opt/remi/php71/root/usr/lib64/php/modules/ /usr/lib64/php/modules/

It is was just a temporary workaroud.
Later, I have updated the broken PHP installation to 7.2: How do I install PHP 7.2 FPM and CLI for Magento 2 to CentOS 7?