You need to assign the short cut, not just execute, press the assign button, an Alert typically comes up, as most short cuts are already set. Besides, it is easy to put a short cut for the Structure Manager accidentally (points/polygons).
I really can’t see what you are doing, so I have to suggest these problems.
Restart the app, hover with the mouse indicator over the icon, the short cut should show up in the “bubble help” if enabled.
Check if you have the rights to change the Preferences. This is an OS problem from time to time. Anything else should be checked with the support.
One suggestion, the 1,2,3 keys are for the Editor view, to move, scale and rotate the area you see. I consider them general short cuts. But it is your set up of course.
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