It's LGPL-2.1-or-later, not GPL.
website_url = "https://www.gtk.org"
authors = "GTK Development Team"
logo_url = "gtk-logo.svg"
-license = "GPL-2.1-or-later"
+license = "LGPL-2.1-or-later"
description = "The GTK toolkit"
dependencies = [ "GObject-2.0", "cairo-1.0", "Pango-1.0", "GdkWayland-4.0", "GdkX11-4.0" ]
devhelp = true
website_url = "https://www.gtk.org"
authors = "GTK Development Team"
logo_url = "gtk-logo.svg"
-license = "GPL-2.1-or-later"
+license = "LGPL-2.1-or-later"
description = "The GTK toolkit"
dependencies = [ "GObject-2.0", "Graphene-1.0", "Pango-1.0", "Gdk-4.0" ]
devhelp = true
website_url = "https://www.gtk.org"
authors = "GTK Development Team"
logo_url = "gtk-logo.svg"
-license = "GPL-2.1-or-later"
+license = "LGPL-2.1-or-later"
description = "The GTK toolkit"
dependencies = [ "GObject-2.0", "Graphene-1.0", "Pango-1.0", "Gdk-4.0", "Gsk-4.0" ]
devhelp = true