PARTLY RESOLVED
I have installed PHP extensions for Redis, Memcached, and APCU but they're not being detected by WordPress.
I have gone as far as opening the ports for the same but still. WordPress can't access the ports.
I'm using Nginx. What could be the issue?
Using CentOS 7
UPDATE
I'm not sure what the problem was. But I have set the website to use PHP version 7.4 (where I have installed the php extensions). But something told me to install the extensions on PHP version 7.3 (powering RoundCube). To my surprise I saw WordPress showing that it now supports Mencached, Redis, and APCU.
So, I decided to check which PHP version is running on WordPress, then I saw its PHP version 7.3 yet I have set version 7.4 from aaPanel. Strange.
Will try to find a fix.