WPGraphQL Meta Query
This extension exposes arguments to PostObject connections allowing for posts to be filtered by meta fields.
Why isn't this in the core WPGraphQL plugin?
Meta Queries can be expensive. They've even been known to take down production sites. Instead of enabling meta queries by default, they've been left out intentionally to allow site owners the chance to critically think about whether or not they would like to support the functionality.
Many sites can support Meta Queries without issue, but many sites can have serious problems if Meta Queries are executed.