Lovestream festival in Bratislava (3 days after Sziget) announced:
The Killers
Martin Garrix
Alt-J
Rag'n'Bone Man
Oscar and the Wolf
Jason Derulo
Editors
Michael Patrick Kelly
I think Nothing But Thieves might still be in game. They are playing some rock festivals in June, which is far from Sziget, but I remember someone talking about them playing Reading & Leeds in other thread. Maybe it's two bands from one leak.
Lovestream festival in Bratislava just announced Imagine Dragons as headliners for 2023 and moved from June to 18-20th August. So I guess they will share headliners with Sziget and Imagine Dragons will be one of them.