Also, you could set the Esc key as an accelerator. That command that you want is esri_mapping_clearSelectionButton.
KoryKramer_1-1666812272790.png
Use that info to find the specific command and assign the Esc key:
KoryKramer_0-1666812229382.png
Then you should be able to hit Esc to clear all selected features in the map.