Dynamically add pop up combo box with a click event

Hi, and welcome to the forum.

I suggest you add a UserForm in the VBE and put a combobox on the form.
Give a name to the range of cells which contain the values you want to use in populating the combobox. If this range varies in size, then you'd be advised to make it a dynamic rage name.

In the combobox properties window, put the name of the Excel range above in the RowSource property

Now again in the VBE add a Module, and within the module a procedure that will Show the UserForm containing the combobox.
i.e.

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In the Excel sheet add a button to run the macro, right click the button and link it to the ShowForm macro

In the VBE, put your code in the ComboBox Click or Change event, and make the last line of this event either
UserForm1.Hide or
Unload UserForm1


HTH