You better disable all the REMI repos that exist on your /etc/yum.repos.d/ folder. Or add the below line in /etc/yum.conf file.
exclude=php*
or
Try this command with yum update.
yum update –exclude=php*
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Run these commands as well.
yum -y reinstall svmstack*
ln -s /usr/local/svmstack/php8/bin/php /usr/bin/php
systemctl restart svmstack-fpm8