Thanks for a bug report, but I'm not much keen into this. the first line in the Guidelines section of the link you gave above reads:
> If an application has more than a few shortcuts, and doesn't have a menu bar,
> it should include a shortcuts window.

The Evolution has the menu bar.

I'm also afraid that the Evolution is too complex for this window (too many items where users can set their own shortcuts as well).

Does GTK's ShortcutWindow actually reads the configuration everytime, or does it hardcode (as shortcuts can be customized, see bug 770141)?

s/bug 770141/bug 780329/ in my previous comment

The GtkShortcuts* widgets are a pain to use in code, because there is no proper API, so you have to poke at GObject properties. I have an open bug for normal API to be added: https://bugzilla.gnome.org/show_bug.cgi?id=770377

Still, if you're OK with doing lots of GObject sets, then it's doable. That bug has an example that I added of how to get a simple GtkShortcutsWindow and children working in C.

I only do this in my app for add-once shortcuts, which are set at startup (alongside the corresponding GActions etc) and then left alone for the entire run, but it's probably possible to remove and readd dynamically.

(or you could be wasteful and rebuild the entire thing every time something changes! but probably better not to ;)

There is no quick reference pdf anymore. Shortcuts are in
https://gitlab.gnome.org/GNOME/evolution/blob/master/help/C/intro-keyboard-shortcuts.page
now.

I would not spend time on a shortcuts window until its new location is sorted out, as the app menus will be removed for 3.32. See
Also see https://mail.gnome.org/archives/desktop-devel-list/2018-September/msg00018.html

I added Keyboard Shortcuts into the Help menu, with shortcuts similar to those in the User Guide.

Created commit [1] in evo master (3.33.4+)

[1] https://gitlab.gnome.org/GNOME/evolution/commit/f41a317fb4