This morning Bitbucket showed me a reminder for the removal of the "List pull requests for a user" endpoint and advises to use the "List workspace pull requests for a user" endpoint (see https://community.atlassian.com/t5/Bitbucket-articles/Reminder-List-pull-requests-for-a-user-API-removal/ba-p/2935311). I tried to migrate to that endpoint, but unfortunately I couldn't find support for the new endpoint in this client yet.

If I'm correct, it should be something like this?

$client->workspaces($workspace)->pullRequests()->list($user, ['q' => $query]);