With the total loss of its Arts Council funding, Hampstead Theatre’s future as a specialist new writing venue is in doubt. But before anything drastically changes, the playwrights and plays developed by Roxana Silbert, who was edged out as artistic director in December last year, are still coming through. One of them is Ruby Thomas, whose Either, her 2019 drama in the studio here, was thrillingly experimental. Boy, can she write! Her latest, this time on the main stage, is Linck & Mülhahn, a historical queer love story which features a gender-pioneering couple.