From the Gnome folks, still very relevant: https://developer.gnome.org/gtk3/stable/gtk-migrating-2-to-3.html

Python script that checks your C source code for deprecated symbols and lists them

Enables you to quickly assess the TODO for a Gtk3 port

Usage: “python3 GtkSymbolCheck.py –gtk_version 3.14 –hide-not-found $folder”

To be found on github: https://github.com/bluesabre/gtk-symbol-check

GTK_STOCK: Use normal translatable strings and icons instead.

Starting with gtk+-3.10 (by this commit), menu accelerators can no longer be changed with gtk-can-change-accels. Possible alternatives yet to be considered: Reimplement that code in custom GtkImageMenuItem, or use a separate dialog like other apps do (using GtkCellRendererAccel and gtk3-Accelerator-Maps). This especially affects thunar which uses this functionality to assign shortcuts to custom actions. If we only want to support this and not editing all other accels, it would be enough to provide a shortcut assign button in the custom actions configuration dialog.

GtkListBox (e.g. for settings; is searchable)

GtkStack (as replacement for GtkNotebook in some contexts)

GtkSwitch (instead of GtkCheckButton in some cases)

GtkPopover for simple single-button menus