Scripts in code/admin/cli/ that begin with mysql_ but they won't fix all yellows. Only character set and collation ... which needs to match the DB array line for db collation and assuring all the tables and columns in tables match.
https is apache config ... does provider offer Let'sEncrypt? or commerial?
DB full unicode support might require setting DB server to use Barracuda and InnoDB
https://docs.moodle.org/39/en/MySQL_full_unicode_support
Zend OpCache is a php extension ... to install ... use operating system package manager to install php-opcache (how one does that dependent upon Operating System)
If you are using something like EasyApache (EA) for choosing version of PHP to use on your moodle, EA might only need to have opcache checked so it is loaded when apache is started.
'SoS', Ken