You can make use of Hotkeys
For Excel - If we have a DropDown - Assuming the DropDown is in Cell A4.
Below would be the Automation steps.
- Send Hotkey : Ctrl G - This will open the Goto Cell menu
- type Into Goto : A4 and Hit Enter - To highlight the Cell having Formula
- Send Hotkey : Alt + DownArrow - This os Open the DropDown.
- Make use of Ui Automation of More hotkeys as required.
Before attempting the above - would request you to Do the Steps manually . If you are able to open Dropdown without using Mouse - Mimic same steps with send Hotkeys.