Thought I'd announce the new library I made, for those not on Gnome, that still want to use Gnome/GTK4/LibAdwaita apps, without the CSD that many of these force on the users. It is similar to gtk3-nocsd, has to be used with LD_PRELOAD. Currently it also depends on X, so on Wayland it needs XWayland.
https://codeberg.org/MorsMortium/GTK4-NoCSD
https://aur.archlinux.org/packages/gtk4-nocsd-git
The library now supports Wayland. The AUR package installs that way, but it can either be modified or just the regular build command used, to disable it, it is completely optional. However, the "key" to changing the headerbar on Wayland is hidden away, so the installer does a single time bruteforce for checking where it will be in the memory. and then it uses that offset for building. It also has a list of well known offsets, currently only having GTK4.18.6, as that is what I have. These offsets are per version, the very least, but might be common among versions