When compiling and installing PHP 7.4, if you use the –with-mbstring parameter, you need to install oniguruma. Oniguruma is a library for handling regular expressions. In PHP 7.4, the mbstring regular expression processing functionality depends on this package. Therefore, you need to install both oniguruma and oniguruma-devel packages before installing PHP 7.4.
The oniguruma and oniguruma-devel packages are not included in most software repositories. You can click:
https://pkgs.org/download/oniguruma
and
https://pkgs.org/download/oniguruma-devel
to download and install them.
Generally, you can install EPEL first and then install them:
yum install -y epel-release
yum install -y oniguruma oniguruma-devel