Gtk3-nocsd support for gtk4 (and libadwaita?) found in ubuntu repos, SSD support and Breeze theme

Brainstorm
1

So apparently ubuntu devs have some git patches to a fork of gtk3-nocsd that implement support for gtk4.
See here https://bugs.launchpad.net/ubuntu/+source/gtk3-nocsd/+bug/1946161

If you search for that patch name with quotes on Google, you’ll end up here

where they provide some debs with the patched version.

To my knowledge this is the only place where you can find some sort of support for gtk4, it doesn’t seem to me to be implemented (libadwaita apps look GNOMEish, not breezeish), but I may be wrong.
Couldn’t make it work tho unfortunately.

Meanwhile I’ve experimented a bit and I’ve forced SSD with a window match rule.
However there was an aweful buggy transparent border between the SSD window boder (with KDE-applied windows’ box-shadows etc) and the GTK window border.
Thru lots of CTRL+SHIFT+D in GTK apps I’ve realized that if you set the property decorated of <appname>MainWindow (or any window) to false, it removes that border!
I tried to inject it via LD_PRELOAD (à la gtk3-nocsd) but no luck so far.

I’ve made some additions to GitHub - MrCompoopter/Libadwaita-Breeze-Dark: A fix of Breeze Dark GTK4 theme made for better compatibility with Flatpak Libadwaita applications and those with the manual setting of decorated to false and the manual removal of buttons via gtk.settings edit give a pretty satisfactory look to Gtk apps with Breeze Dark.
My additions, before their CSS:

window {
	border-radius: unset;
	box-shadow: unset;
}

window.csd {
	border-radius: unset;
	box-shadow: unset;
}

window.csd:backdrop {
	box-shadow: unset;
	transition: unset;
}

window.tiled,
window.tiled-right,
window.tiled-top,
window.tiled-left,
window.tiled-bottom {
	border-radius: unset;
	box-shadow: unset;
}


window.tiled:backdrop,
window.tiled-right:backdrop,
window.tiled-top:backdrop,
window.tiled-left:backdrop,
window.tiled-bottom:backdrop {
	border-radius: unset;
	box-shadow: unset;
}

window.solid-csd {
	box-shadow: unset;
	padding: unset;
}

window.solid-csd:backdrop {
	box-shadow: unset;
}

window.ssd {
	box-shadow: unset;
}

window.dialog.message,
window.messagedialog {
	box-shadow: unset;
}

window.main-page > viewport > clamp > box {
	margin: unset;
}

(Btw, wouldn’t it be easier to just fork GTK, apply these patches we would via *nocsd injector and use that instead? It would require coordination with distros I guess but maybe that’s easier than having hacks?)