libxml_disable_entity_loader() calls are used in MediaWiki and dependencies to prevent XXE injection vulnerabilities when processing arbitrary XML code. In PHP 8 and above, PHP uses a newer version of libxml that disables XXE loading by default, and PHP now raises a deprecation message when this function is called:
Deprecated: Function libxml_disable_entity_loader() is deprecated in ... on line ...
MediaWiki code and dependencies' code will need to be updated, probably by making this call conditional on PHP/libxml version.