Thanks @vanvugt, so there are 3 UI ways of hiding the desktop icons, but only one works:
$ gnome-shell-extension-prefs
... then switch off the desktop-icons extension.
(Nevermind that gnome tweaks, under "Extensions", listed the desktop-icons gnome shell extension as disabled.)
The bugs are then the mere existence of the other two UI ways of hiding desktop icons.
Thanks @vanvugt, so there are 3 UI ways of hiding the desktop icons, but only one works:
$ gnome-shell- extension- prefs
... then switch off the desktop-icons extension.
(Nevermind that gnome tweaks, under "Extensions", listed the desktop-icons gnome shell extension as disabled.)
The bugs are then the mere existence of the other two UI ways of hiding desktop icons.