In order to support Wayland properly, client-side decorations are necessary; the xdg-decorations protocol lets the application ask the compositor to draw CSDs, but the compositor is allowed to refuse and demand the application draws its own decorations.
Has anyone experimented with bringing a CSD fallback to SDL? If so, I’d be interested in trying it out and contributing.
(Also, please don’t discuss why CSDs are stupid. I wish compositors like GNOME’s Mutter would just draw SSDs when asked to, but they don’t, and the protocol says they don’t have to. Therefore, SDL needs CSDs as a fallback. The discussion about whether it should be like that is off-topic in this thread.)