Honor keyboard accelerators
In attempting to set a keyboard shortcut for clear all selected features, I am having a hard time. My first choice, Ctrl+Shift+A, simply did not work. My second choice, Ctrl+D, asked me if I want to override the Delete shortcut. Since I have a delete key, I am more than fine with this and click Yes. I click OK, and go to my map and press Ctrl+D. What does it do? Ask if I want to delete features. I go back to settings and find that it has lost my accelerator. Please honor custom accelerators, thanks.
In ArcGIS Pro 3.1.2 I did what you're describing.
Right-clicking on that Clear button > Copy Command ID should give you esri_mapping_clearSelectionButton.
Go to customize the ribbon > All Commands and search for that. I was able to set it to Ctrl+Shift+A and it works.
What are we missing?
I went about it this way, is that different?
I can't be 100% sure from your screenshot, but when I hover over Clear (Clear selection of all features) with the 'Show command IDs on ScreenTips' on, I see that it has something to do with raster layers.
This is why it can help to grab the specific command ID from the command first and search using that - it is unambiguous. (Yes, I saw your idea about grabbing that for Editing tools 🙂 )
Please try the above and let me know if it is working for you.