Have you somehow managed to install PHP from both SCL and Remi repos? If so, make sure that you don’t have the same versions installed at the same time.
Anyway, I now see that your virtual server is currently using rh-php73 in FastCGI mode. The solution to your problem would be as simple as running the following commands:
yum install sclo-php73-php-pecl-memcached
systemctl restart httpd