To reproduce: bind a couple of alternative keys in the key binds menu, then go back and re-open the keybinds menu. This is the result after adding alternative keybinds (numpad 1-9) to the hotbar slot keys, then clicking done and reopening the key binds menu:
I have confirmed this not to be the case in the normal NMUK for 1.20.3.
To reproduce: bind a couple of alternative keys in the key binds menu, then go back and re-open the keybinds menu. This is the result after adding alternative keybinds (numpad 1-9) to the hotbar slot keys, then clicking done and reopening the key binds menu:
I have confirmed this not to be the case in the normal NMUK for 1.20.3.