Fatal error: Declaration of MediaWiki\Rest\Response::getStatusCode() must be compatible with Psr\Http\Message\ResponseInterface::getStatusCode(): int in /web/wiki/extensions/OAuth/src/Response.php on line 36
Similar to T335073 and T333993, OAuth extension broke after composer update, or install from tarball.
It seems to league/oauth2-server package require psr/http-message 1.1 version.
I'm using mediawiki 1.39.4 and Oauth extension REL1_39 branch on php 7.4.