Keyboard accelerators for window menus aren't implemented
See https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1710421 for the original bug report.
Other desktop systems including Microsoft Windows and Unity have accelerator keys in the window menu. This is typically accessible via ALT_Space on any window, then pressing a key to initiate the desired function.
Typically Alt_Space can be used to bring up the menu, then use x to maximise a window, n to minimise a window, etc. GNOME Shell does not implement these accelerator keys, which seems inconsistent with other desktops, and internally inconsistent, as other menus in GNOME applications do have accelerator keys.
It would be great for people coming to GNOME Shell should be able to use the familiar keyboard shortcuts they're used to.
As far as I can test (as far back as 16.04) this has always been the case.