Came across this very downstream (generating stubfiles for WPGraphQL.

Tl;dr: GraphQL\Type\Definition\Deprecated uses a public string as its arg, but Constructor Promotion is only available in PHP8+ (https://www.php.net/manual/en/language.oop5.decon.php).

I'm not sure how real this issue besides the failing downstream lint (https://github.com/AxeWP/wp-graphql-stubs/actions/runs/21398618877/job/61603298081). If it is real, the solution is simply to manually define the class prop and assign it in the constructor.

Also assumedly, setting PHPStan's phpversion with a minVersion: 70400 would prevent this sort of smell (PHP incompatibility with a version lower than the one CI is stanning) in the future.